Documentation / glossary-content.txton commit regex: use regexec_buf() (b7d36ff)
   1[[def_alternate_object_database]]alternate object database::
   2        Via the alternates mechanism, a <<def_repository,repository>>
   3        can inherit part of its <<def_object_database,object database>>
   4        from another object database, which is called an "alternate".
   5
   6[[def_bare_repository]]bare repository::
   7        A bare repository is normally an appropriately
   8        named <<def_directory,directory>> with a `.git` suffix that does not
   9        have a locally checked-out copy of any of the files under
  10        revision control. That is, all of the Git
  11        administrative and control files that would normally be present in the
  12        hidden `.git` sub-directory are directly present in the
  13        `repository.git` directory instead,
  14        and no other files are present and checked out. Usually publishers of
  15        public repositories make bare repositories available.
  16
  17[[def_blob_object]]blob object::
  18        Untyped <<def_object,object>>, e.g. the contents of a file.
  19
  20[[def_branch]]branch::
  21        A "branch" is an active line of development.  The most recent
  22        <<def_commit,commit>> on a branch is referred to as the tip of
  23        that branch.  The tip of the branch is referenced by a branch
  24        <<def_head,head>>, which moves forward as additional development
  25        is done on the branch.  A single Git
  26        <<def_repository,repository>> can track an arbitrary number of
  27        branches, but your <<def_working_tree,working tree>> is
  28        associated with just one of them (the "current" or "checked out"
  29        branch), and <<def_HEAD,HEAD>> points to that branch.
  30
  31[[def_cache]]cache::
  32        Obsolete for: <<def_index,index>>.
  33
  34[[def_chain]]chain::
  35        A list of objects, where each <<def_object,object>> in the list contains
  36        a reference to its successor (for example, the successor of a
  37        <<def_commit,commit>> could be one of its <<def_parent,parents>>).
  38
  39[[def_changeset]]changeset::
  40        BitKeeper/cvsps speak for "<<def_commit,commit>>". Since Git does not
  41        store changes, but states, it really does not make sense to use the term
  42        "changesets" with Git.
  43
  44[[def_checkout]]checkout::
  45        The action of updating all or part of the
  46        <<def_working_tree,working tree>> with a <<def_tree_object,tree object>>
  47        or <<def_blob_object,blob>> from the
  48        <<def_object_database,object database>>, and updating the
  49        <<def_index,index>> and <<def_HEAD,HEAD>> if the whole working tree has
  50        been pointed at a new <<def_branch,branch>>.
  51
  52[[def_cherry-picking]]cherry-picking::
  53        In <<def_SCM,SCM>> jargon, "cherry pick" means to choose a subset of
  54        changes out of a series of changes (typically commits) and record them
  55        as a new series of changes on top of a different codebase. In Git, this is
  56        performed by the "git cherry-pick" command to extract the change introduced
  57        by an existing <<def_commit,commit>> and to record it based on the tip
  58        of the current <<def_branch,branch>> as a new commit.
  59
  60[[def_clean]]clean::
  61        A <<def_working_tree,working tree>> is clean, if it
  62        corresponds to the <<def_revision,revision>> referenced by the current
  63        <<def_head,head>>. Also see "<<def_dirty,dirty>>".
  64
  65[[def_commit]]commit::
  66        As a noun: A single point in the
  67        Git history; the entire history of a project is represented as a
  68        set of interrelated commits.  The word "commit" is often
  69        used by Git in the same places other revision control systems
  70        use the words "revision" or "version".  Also used as a short
  71        hand for <<def_commit_object,commit object>>.
  72+
  73As a verb: The action of storing a new snapshot of the project's
  74state in the Git history, by creating a new commit representing the current
  75state of the <<def_index,index>> and advancing <<def_HEAD,HEAD>>
  76to point at the new commit.
  77
  78[[def_commit_object]]commit object::
  79        An <<def_object,object>> which contains the information about a
  80        particular <<def_revision,revision>>, such as <<def_parent,parents>>, committer,
  81        author, date and the <<def_tree_object,tree object>> which corresponds
  82        to the top <<def_directory,directory>> of the stored
  83        revision.
  84
  85[[def_commit-ish]]commit-ish (also committish)::
  86        A <<def_commit_object,commit object>> or an
  87        <<def_object,object>> that can be recursively dereferenced to
  88        a commit object.
  89        The following are all commit-ishes:
  90        a commit object,
  91        a <<def_tag_object,tag object>> that points to a commit
  92        object,
  93        a tag object that points to a tag object that points to a
  94        commit object,
  95        etc.
  96
  97[[def_core_git]]core Git::
  98        Fundamental data structures and utilities of Git. Exposes only limited
  99        source code management tools.
 100
 101[[def_DAG]]DAG::
 102        Directed acyclic graph. The <<def_commit_object,commit objects>> form a
 103        directed acyclic graph, because they have parents (directed), and the
 104        graph of commit objects is acyclic (there is no <<def_chain,chain>>
 105        which begins and ends with the same <<def_object,object>>).
 106
 107[[def_dangling_object]]dangling object::
 108        An <<def_unreachable_object,unreachable object>> which is not
 109        <<def_reachable,reachable>> even from other unreachable objects; a
 110        dangling object has no references to it from any
 111        reference or <<def_object,object>> in the <<def_repository,repository>>.
 112
 113[[def_detached_HEAD]]detached HEAD::
 114        Normally the <<def_HEAD,HEAD>> stores the name of a
 115        <<def_branch,branch>>, and commands that operate on the
 116        history HEAD represents operate on the history leading to the
 117        tip of the branch the HEAD points at.  However, Git also
 118        allows you to <<def_checkout,check out>> an arbitrary
 119        <<def_commit,commit>> that isn't necessarily the tip of any
 120        particular branch.  The HEAD in such a state is called
 121        "detached".
 122+
 123Note that commands that operate on the history of the current branch
 124(e.g. `git commit` to build a new history on top of it) still work
 125while the HEAD is detached. They update the HEAD to point at the tip
 126of the updated history without affecting any branch.  Commands that
 127update or inquire information _about_ the current branch (e.g. `git
 128branch --set-upstream-to` that sets what remote-tracking branch the
 129current branch integrates with) obviously do not work, as there is no
 130(real) current branch to ask about in this state.
 131
 132[[def_directory]]directory::
 133        The list you get with "ls" :-)
 134
 135[[def_dirty]]dirty::
 136        A <<def_working_tree,working tree>> is said to be "dirty" if
 137        it contains modifications which have not been <<def_commit,committed>> to the current
 138        <<def_branch,branch>>.
 139
 140[[def_evil_merge]]evil merge::
 141        An evil merge is a <<def_merge,merge>> that introduces changes that
 142        do not appear in any <<def_parent,parent>>.
 143
 144[[def_fast_forward]]fast-forward::
 145        A fast-forward is a special type of <<def_merge,merge>> where you have a
 146        <<def_revision,revision>> and you are "merging" another
 147        <<def_branch,branch>>'s changes that happen to be a descendant of what
 148        you have. In such a case, you do not make a new <<def_merge,merge>>
 149        <<def_commit,commit>> but instead just update to his
 150        revision. This will happen frequently on a
 151        <<def_remote_tracking_branch,remote-tracking branch>> of a remote
 152        <<def_repository,repository>>.
 153
 154[[def_fetch]]fetch::
 155        Fetching a <<def_branch,branch>> means to get the
 156        branch's <<def_head_ref,head ref>> from a remote
 157        <<def_repository,repository>>, to find out which objects are
 158        missing from the local <<def_object_database,object database>>,
 159        and to get them, too.  See also linkgit:git-fetch[1].
 160
 161[[def_file_system]]file system::
 162        Linus Torvalds originally designed Git to be a user space file system,
 163        i.e. the infrastructure to hold files and directories. That ensured the
 164        efficiency and speed of Git.
 165
 166[[def_git_archive]]Git archive::
 167        Synonym for <<def_repository,repository>> (for arch people).
 168
 169[[def_gitfile]]gitfile::
 170        A plain file `.git` at the root of a working tree that
 171        points at the directory that is the real repository.
 172
 173[[def_grafts]]grafts::
 174        Grafts enables two otherwise different lines of development to be joined
 175        together by recording fake ancestry information for commits. This way
 176        you can make Git pretend the set of <<def_parent,parents>> a <<def_commit,commit>> has
 177        is different from what was recorded when the commit was
 178        created. Configured via the `.git/info/grafts` file.
 179+
 180Note that the grafts mechanism is outdated and can lead to problems
 181transferring objects between repositories; see linkgit:git-replace[1]
 182for a more flexible and robust system to do the same thing.
 183
 184[[def_hash]]hash::
 185        In Git's context, synonym for <<def_object_name,object name>>.
 186
 187[[def_head]]head::
 188        A <<def_ref,named reference>> to the <<def_commit,commit>> at the tip of a
 189        <<def_branch,branch>>.  Heads are stored in a file in
 190        `$GIT_DIR/refs/heads/` directory, except when using packed refs. (See
 191        linkgit:git-pack-refs[1].)
 192
 193[[def_HEAD]]HEAD::
 194        The current <<def_branch,branch>>.  In more detail: Your <<def_working_tree,
 195        working tree>> is normally derived from the state of the tree
 196        referred to by HEAD.  HEAD is a reference to one of the
 197        <<def_head,heads>> in your repository, except when using a
 198        <<def_detached_HEAD,detached HEAD>>, in which case it directly
 199        references an arbitrary commit.
 200
 201[[def_head_ref]]head ref::
 202        A synonym for <<def_head,head>>.
 203
 204[[def_hook]]hook::
 205        During the normal execution of several Git commands, call-outs are made
 206        to optional scripts that allow a developer to add functionality or
 207        checking. Typically, the hooks allow for a command to be pre-verified
 208        and potentially aborted, and allow for a post-notification after the
 209        operation is done. The hook scripts are found in the
 210        `$GIT_DIR/hooks/` directory, and are enabled by simply
 211        removing the `.sample` suffix from the filename. In earlier versions
 212        of Git you had to make them executable.
 213
 214[[def_index]]index::
 215        A collection of files with stat information, whose contents are stored
 216        as objects. The index is a stored version of your
 217        <<def_working_tree,working tree>>. Truth be told, it can also contain a second, and even
 218        a third version of a working tree, which are used
 219        when <<def_merge,merging>>.
 220
 221[[def_index_entry]]index entry::
 222        The information regarding a particular file, stored in the
 223        <<def_index,index>>. An index entry can be unmerged, if a
 224        <<def_merge,merge>> was started, but not yet finished (i.e. if
 225        the index contains multiple versions of that file).
 226
 227[[def_master]]master::
 228        The default development <<def_branch,branch>>. Whenever you
 229        create a Git <<def_repository,repository>>, a branch named
 230        "master" is created, and becomes the active branch. In most
 231        cases, this contains the local development, though that is
 232        purely by convention and is not required.
 233
 234[[def_merge]]merge::
 235        As a verb: To bring the contents of another
 236        <<def_branch,branch>> (possibly from an external
 237        <<def_repository,repository>>) into the current branch.  In the
 238        case where the merged-in branch is from a different repository,
 239        this is done by first <<def_fetch,fetching>> the remote branch
 240        and then merging the result into the current branch.  This
 241        combination of fetch and merge operations is called a
 242        <<def_pull,pull>>.  Merging is performed by an automatic process
 243        that identifies changes made since the branches diverged, and
 244        then applies all those changes together.  In cases where changes
 245        conflict, manual intervention may be required to complete the
 246        merge.
 247+
 248As a noun: unless it is a <<def_fast_forward,fast-forward>>, a
 249successful merge results in the creation of a new <<def_commit,commit>>
 250representing the result of the merge, and having as
 251<<def_parent,parents>> the tips of the merged <<def_branch,branches>>.
 252This commit is referred to as a "merge commit", or sometimes just a
 253"merge".
 254
 255[[def_object]]object::
 256        The unit of storage in Git. It is uniquely identified by the
 257        <<def_SHA1,SHA-1>> of its contents. Consequently, an
 258        object can not be changed.
 259
 260[[def_object_database]]object database::
 261        Stores a set of "objects", and an individual <<def_object,object>> is
 262        identified by its <<def_object_name,object name>>. The objects usually
 263        live in `$GIT_DIR/objects/`.
 264
 265[[def_object_identifier]]object identifier::
 266        Synonym for <<def_object_name,object name>>.
 267
 268[[def_object_name]]object name::
 269        The unique identifier of an <<def_object,object>>.  The
 270        object name is usually represented by a 40 character
 271        hexadecimal string.  Also colloquially called <<def_SHA1,SHA-1>>.
 272
 273[[def_object_type]]object type::
 274        One of the identifiers "<<def_commit_object,commit>>",
 275        "<<def_tree_object,tree>>", "<<def_tag_object,tag>>" or
 276        "<<def_blob_object,blob>>" describing the type of an
 277        <<def_object,object>>.
 278
 279[[def_octopus]]octopus::
 280        To <<def_merge,merge>> more than two <<def_branch,branches>>.
 281
 282[[def_origin]]origin::
 283        The default upstream <<def_repository,repository>>. Most projects have
 284        at least one upstream project which they track. By default
 285        'origin' is used for that purpose. New upstream updates
 286        will be fetched into <<def_remote_tracking_branch,remote-tracking branches>> named
 287        origin/name-of-upstream-branch, which you can see using
 288        `git branch -r`.
 289
 290[[def_pack]]pack::
 291        A set of objects which have been compressed into one file (to save space
 292        or to transmit them efficiently).
 293
 294[[def_pack_index]]pack index::
 295        The list of identifiers, and other information, of the objects in a
 296        <<def_pack,pack>>, to assist in efficiently accessing the contents of a
 297        pack.
 298
 299[[def_pathspec]]pathspec::
 300        Pattern used to limit paths in Git commands.
 301+
 302Pathspecs are used on the command line of "git ls-files", "git
 303ls-tree", "git add", "git grep", "git diff", "git checkout",
 304and many other commands to
 305limit the scope of operations to some subset of the tree or
 306worktree.  See the documentation of each command for whether
 307paths are relative to the current directory or toplevel.  The
 308pathspec syntax is as follows:
 309+
 310--
 311
 312* any path matches itself
 313* the pathspec up to the last slash represents a
 314  directory prefix.  The scope of that pathspec is
 315  limited to that subtree.
 316* the rest of the pathspec is a pattern for the remainder
 317  of the pathname.  Paths relative to the directory
 318  prefix will be matched against that pattern using fnmatch(3);
 319  in particular, '*' and '?' _can_ match directory separators.
 320
 321--
 322+
 323For example, Documentation/*.jpg will match all .jpg files
 324in the Documentation subtree,
 325including Documentation/chapter_1/figure_1.jpg.
 326+
 327A pathspec that begins with a colon `:` has special meaning.  In the
 328short form, the leading colon `:` is followed by zero or more "magic
 329signature" letters (which optionally is terminated by another colon `:`),
 330and the remainder is the pattern to match against the path.
 331The "magic signature" consists of ASCII symbols that are neither
 332alphanumeric, glob, regex special characters nor colon.
 333The optional colon that terminates the "magic signature" can be
 334omitted if the pattern begins with a character that does not belong to
 335"magic signature" symbol set and is not a colon.
 336+
 337In the long form, the leading colon `:` is followed by a open
 338parenthesis `(`, a comma-separated list of zero or more "magic words",
 339and a close parentheses `)`, and the remainder is the pattern to match
 340against the path.
 341+
 342A pathspec with only a colon means "there is no pathspec". This form
 343should not be combined with other pathspec.
 344+
 345--
 346top;;
 347        The magic word `top` (magic signature: `/`) makes the pattern
 348        match from the root of the working tree, even when you are
 349        running the command from inside a subdirectory.
 350
 351literal;;
 352        Wildcards in the pattern such as `*` or `?` are treated
 353        as literal characters.
 354
 355icase;;
 356        Case insensitive match.
 357
 358glob;;
 359        Git treats the pattern as a shell glob suitable for
 360        consumption by fnmatch(3) with the FNM_PATHNAME flag:
 361        wildcards in the pattern will not match a / in the pathname.
 362        For example, "Documentation/{asterisk}.html" matches
 363        "Documentation/git.html" but not "Documentation/ppc/ppc.html"
 364        or "tools/perf/Documentation/perf.html".
 365+
 366Two consecutive asterisks ("`**`") in patterns matched against
 367full pathname may have special meaning:
 368
 369 - A leading "`**`" followed by a slash means match in all
 370   directories. For example, "`**/foo`" matches file or directory
 371   "`foo`" anywhere, the same as pattern "`foo`". "`**/foo/bar`"
 372   matches file or directory "`bar`" anywhere that is directly
 373   under directory "`foo`".
 374
 375 - A trailing "`/**`" matches everything inside. For example,
 376   "`abc/**`" matches all files inside directory "abc", relative
 377   to the location of the `.gitignore` file, with infinite depth.
 378
 379 - A slash followed by two consecutive asterisks then a slash
 380   matches zero or more directories. For example, "`a/**/b`"
 381   matches "`a/b`", "`a/x/b`", "`a/x/y/b`" and so on.
 382
 383 - Other consecutive asterisks are considered invalid.
 384+
 385Glob magic is incompatible with literal magic.
 386
 387exclude;;
 388        After a path matches any non-exclude pathspec, it will be run
 389        through all exclude pathspec (magic signature: `!`). If it
 390        matches, the path is ignored.
 391--
 392
 393[[def_parent]]parent::
 394        A <<def_commit_object,commit object>> contains a (possibly empty) list
 395        of the logical predecessor(s) in the line of development, i.e. its
 396        parents.
 397
 398[[def_pickaxe]]pickaxe::
 399        The term <<def_pickaxe,pickaxe>> refers to an option to the diffcore
 400        routines that help select changes that add or delete a given text
 401        string. With the `--pickaxe-all` option, it can be used to view the full
 402        <<def_changeset,changeset>> that introduced or removed, say, a
 403        particular line of text. See linkgit:git-diff[1].
 404
 405[[def_plumbing]]plumbing::
 406        Cute name for <<def_core_git,core Git>>.
 407
 408[[def_porcelain]]porcelain::
 409        Cute name for programs and program suites depending on
 410        <<def_core_git,core Git>>, presenting a high level access to
 411        core Git. Porcelains expose more of a <<def_SCM,SCM>>
 412        interface than the <<def_plumbing,plumbing>>.
 413
 414[[def_per_worktree_ref]]per-worktree ref::
 415        Refs that are per-<<def_working_tree,worktree>>, rather than
 416        global.  This is presently only <<def_HEAD,HEAD>> and any refs
 417        that start with `refs/bisect/`, but might later include other
 418        unusual refs.
 419
 420[[def_pseudoref]]pseudoref::
 421        Pseudorefs are a class of files under `$GIT_DIR` which behave
 422        like refs for the purposes of rev-parse, but which are treated
 423        specially by git.  Pseudorefs both have names that are all-caps,
 424        and always start with a line consisting of a
 425        <<def_SHA1,SHA-1>> followed by whitespace.  So, HEAD is not a
 426        pseudoref, because it is sometimes a symbolic ref.  They might
 427        optionally contain some additional data.  `MERGE_HEAD` and
 428        `CHERRY_PICK_HEAD` are examples.  Unlike
 429        <<def_per_worktree_ref,per-worktree refs>>, these files cannot
 430        be symbolic refs, and never have reflogs.  They also cannot be
 431        updated through the normal ref update machinery.  Instead,
 432        they are updated by directly writing to the files.  However,
 433        they can be read as if they were refs, so `git rev-parse
 434        MERGE_HEAD` will work.
 435
 436[[def_pull]]pull::
 437        Pulling a <<def_branch,branch>> means to <<def_fetch,fetch>> it and
 438        <<def_merge,merge>> it.  See also linkgit:git-pull[1].
 439
 440[[def_push]]push::
 441        Pushing a <<def_branch,branch>> means to get the branch's
 442        <<def_head_ref,head ref>> from a remote <<def_repository,repository>>,
 443        find out if it is a direct ancestor to the branch's local
 444        head ref, and in that case, putting all
 445        objects, which are <<def_reachable,reachable>> from the local
 446        head ref, and which are missing from the remote
 447        repository, into the remote
 448        <<def_object_database,object database>>, and updating the remote
 449        head ref. If the remote <<def_head,head>> is not an
 450        ancestor to the local head, the push fails.
 451
 452[[def_reachable]]reachable::
 453        All of the ancestors of a given <<def_commit,commit>> are said to be
 454        "reachable" from that commit. More
 455        generally, one <<def_object,object>> is reachable from
 456        another if we can reach the one from the other by a <<def_chain,chain>>
 457        that follows <<def_tag,tags>> to whatever they tag,
 458        <<def_commit_object,commits>> to their parents or trees, and
 459        <<def_tree_object,trees>> to the trees or <<def_blob_object,blobs>>
 460        that they contain.
 461
 462[[def_rebase]]rebase::
 463        To reapply a series of changes from a <<def_branch,branch>> to a
 464        different base, and reset the <<def_head,head>> of that branch
 465        to the result.
 466
 467[[def_ref]]ref::
 468        A name that begins with `refs/` (e.g. `refs/heads/master`)
 469        that points to an <<def_object_name,object name>> or another
 470        ref (the latter is called a <<def_symref,symbolic ref>>).
 471        For convenience, a ref can sometimes be abbreviated when used
 472        as an argument to a Git command; see linkgit:gitrevisions[7]
 473        for details.
 474        Refs are stored in the <<def_repository,repository>>.
 475+
 476The ref namespace is hierarchical.
 477Different subhierarchies are used for different purposes (e.g. the
 478`refs/heads/` hierarchy is used to represent local branches).
 479+
 480There are a few special-purpose refs that do not begin with `refs/`.
 481The most notable example is `HEAD`.
 482
 483[[def_reflog]]reflog::
 484        A reflog shows the local "history" of a ref.  In other words,
 485        it can tell you what the 3rd last revision in _this_ repository
 486        was, and what was the current state in _this_ repository,
 487        yesterday 9:14pm.  See linkgit:git-reflog[1] for details.
 488
 489[[def_refspec]]refspec::
 490        A "refspec" is used by <<def_fetch,fetch>> and
 491        <<def_push,push>> to describe the mapping between remote
 492        <<def_ref,ref>> and local ref.
 493
 494[[def_remote]]remote repository::
 495        A <<def_repository,repository>> which is used to track the same
 496        project but resides somewhere else. To communicate with remotes,
 497        see <<def_fetch,fetch>> or <<def_push,push>>.
 498
 499[[def_remote_tracking_branch]]remote-tracking branch::
 500        A <<def_ref,ref>> that is used to follow changes from another
 501        <<def_repository,repository>>. It typically looks like
 502        'refs/remotes/foo/bar' (indicating that it tracks a branch named
 503        'bar' in a remote named 'foo'), and matches the right-hand-side of
 504        a configured fetch <<def_refspec,refspec>>. A remote-tracking
 505        branch should not contain direct modifications or have local
 506        commits made to it.
 507
 508[[def_repository]]repository::
 509        A collection of <<def_ref,refs>> together with an
 510        <<def_object_database,object database>> containing all objects
 511        which are <<def_reachable,reachable>> from the refs, possibly
 512        accompanied by meta data from one or more <<def_porcelain,porcelains>>. A
 513        repository can share an object database with other repositories
 514        via <<def_alternate_object_database,alternates mechanism>>.
 515
 516[[def_resolve]]resolve::
 517        The action of fixing up manually what a failed automatic
 518        <<def_merge,merge>> left behind.
 519
 520[[def_revision]]revision::
 521        Synonym for <<def_commit,commit>> (the noun).
 522
 523[[def_rewind]]rewind::
 524        To throw away part of the development, i.e. to assign the
 525        <<def_head,head>> to an earlier <<def_revision,revision>>.
 526
 527[[def_SCM]]SCM::
 528        Source code management (tool).
 529
 530[[def_SHA1]]SHA-1::
 531        "Secure Hash Algorithm 1"; a cryptographic hash function.
 532        In the context of Git used as a synonym for <<def_object_name,object name>>.
 533
 534[[def_shallow_clone]]shallow clone::
 535        Mostly a synonym to <<def_shallow_repository,shallow repository>>
 536        but the phrase makes it more explicit that it was created by
 537        running `git clone --depth=...` command.
 538
 539[[def_shallow_repository]]shallow repository::
 540        A shallow <<def_repository,repository>> has an incomplete
 541        history some of whose <<def_commit,commits>> have <<def_parent,parents>> cauterized away (in other
 542        words, Git is told to pretend that these commits do not have the
 543        parents, even though they are recorded in the <<def_commit_object,commit
 544        object>>). This is sometimes useful when you are interested only in the
 545        recent history of a project even though the real history recorded in the
 546        upstream is much larger. A shallow repository
 547        is created by giving the `--depth` option to linkgit:git-clone[1], and
 548        its history can be later deepened with linkgit:git-fetch[1].
 549
 550[[def_submodule]]submodule::
 551        A <<def_repository,repository>> that holds the history of a
 552        separate project inside another repository (the latter of
 553        which is called <<def_superproject, superproject>>).
 554
 555[[def_superproject]]superproject::
 556        A <<def_repository,repository>> that references repositories
 557        of other projects in its working tree as <<def_submodule,submodules>>.
 558        The superproject knows about the names of (but does not hold
 559        copies of) commit objects of the contained submodules.
 560
 561[[def_symref]]symref::
 562        Symbolic reference: instead of containing the <<def_SHA1,SHA-1>>
 563        id itself, it is of the format 'ref: refs/some/thing' and when
 564        referenced, it recursively dereferences to this reference.
 565        '<<def_HEAD,HEAD>>' is a prime example of a symref. Symbolic
 566        references are manipulated with the linkgit:git-symbolic-ref[1]
 567        command.
 568
 569[[def_tag]]tag::
 570        A <<def_ref,ref>> under `refs/tags/` namespace that points to an
 571        object of an arbitrary type (typically a tag points to either a
 572        <<def_tag_object,tag>> or a <<def_commit_object,commit object>>).
 573        In contrast to a <<def_head,head>>, a tag is not updated by
 574        the `commit` command. A Git tag has nothing to do with a Lisp
 575        tag (which would be called an <<def_object_type,object type>>
 576        in Git's context). A tag is most typically used to mark a particular
 577        point in the commit ancestry <<def_chain,chain>>.
 578
 579[[def_tag_object]]tag object::
 580        An <<def_object,object>> containing a <<def_ref,ref>> pointing to
 581        another object, which can contain a message just like a
 582        <<def_commit_object,commit object>>. It can also contain a (PGP)
 583        signature, in which case it is called a "signed tag object".
 584
 585[[def_topic_branch]]topic branch::
 586        A regular Git <<def_branch,branch>> that is used by a developer to
 587        identify a conceptual line of development. Since branches are very easy
 588        and inexpensive, it is often desirable to have several small branches
 589        that each contain very well defined concepts or small incremental yet
 590        related changes.
 591
 592[[def_tree]]tree::
 593        Either a <<def_working_tree,working tree>>, or a <<def_tree_object,tree
 594        object>> together with the dependent <<def_blob_object,blob>> and tree objects
 595        (i.e. a stored representation of a working tree).
 596
 597[[def_tree_object]]tree object::
 598        An <<def_object,object>> containing a list of file names and modes along
 599        with refs to the associated blob and/or tree objects. A
 600        <<def_tree,tree>> is equivalent to a <<def_directory,directory>>.
 601
 602[[def_tree-ish]]tree-ish (also treeish)::
 603        A <<def_tree_object,tree object>> or an <<def_object,object>>
 604        that can be recursively dereferenced to a tree object.
 605        Dereferencing a <<def_commit_object,commit object>> yields the
 606        tree object corresponding to the <<def_revision,revision>>'s
 607        top <<def_directory,directory>>.
 608        The following are all tree-ishes:
 609        a <<def_commit-ish,commit-ish>>,
 610        a tree object,
 611        a <<def_tag_object,tag object>> that points to a tree object,
 612        a tag object that points to a tag object that points to a tree
 613        object,
 614        etc.
 615
 616[[def_unmerged_index]]unmerged index::
 617        An <<def_index,index>> which contains unmerged
 618        <<def_index_entry,index entries>>.
 619
 620[[def_unreachable_object]]unreachable object::
 621        An <<def_object,object>> which is not <<def_reachable,reachable>> from a
 622        <<def_branch,branch>>, <<def_tag,tag>>, or any other reference.
 623
 624[[def_upstream_branch]]upstream branch::
 625        The default <<def_branch,branch>> that is merged into the branch in
 626        question (or the branch in question is rebased onto). It is configured
 627        via branch.<name>.remote and branch.<name>.merge. If the upstream branch
 628        of 'A' is 'origin/B' sometimes we say "'A' is tracking 'origin/B'".
 629
 630[[def_working_tree]]working tree::
 631        The tree of actual checked out files.  The working tree normally
 632        contains the contents of the <<def_HEAD,HEAD>> commit's tree,
 633        plus any local changes that you have made but not yet committed.