-A packed archive is an efficient way to transfer set of objects
-between two repositories, and also is an archival format which
-is efficient to access. The packed archive format (.pack) is
-designed to be self contained so that it can be unpacked without
-any further information, but for fast, random access to the objects
-in the pack, a pack index file (.idx) will be generated.
-
-Placing both in the pack/ subdirectory of $GIT_OBJECT_DIRECTORY (or
+A packed archive is an efficient way to transfer a set of objects
+between two repositories as well as an access efficient archival
+format. In a packed archive, an object is either stored as a
+compressed whole or as a difference from some other object.
+The latter is often called a delta.
+
+The packed archive format (.pack) is designed to be self-contained
+so that it can be unpacked without any further information. Therefore,
+each object that a delta depends upon must be present within the pack.
+
+A pack index file (.idx) is generated for fast, random access to the
+objects in the pack. Placing both the index file (.idx) and the packed
+archive (.pack) in the pack/ subdirectory of $GIT_OBJECT_DIRECTORY (or