The Jargon File (version 4.4.7, 29 Dec 2003):

diff
 /dif/, n.

    1. A change listing, especially giving differences between (and additions
    to) source code or documents (the term is often used in the plural diffs).
    ?Send me your diffs for the Jargon File!? Compare vdiff.

    2. Specifically, such a listing produced by the diff(1) command, esp. when
    used as specification input to the patch(1) utility (which can actually
    perform the modifications; see patch). This is a common method of
    distributing patches and source updates in the Unix/C world.

    3. v. To compare (whether or not by use of automated tools on
    machine-readable files); see also vdiff, mod.


The Free On-line Dictionary of Computing (30 December 2018):

diff

   /dif/ 1. A change listing, especially giving differences
   between (and additions to) different versions of a piece of
   source code or documentation (the term is often used in the
   plural "diffs").  "Send me your diffs for the Jargon File!"

   Compare vdiff.

   2. Specifically, such a listing produced by the diff Unix
   command, especially when used as input to the patch utility
   (which actually performs the modifications).  This is a common
   method of distributing patches and source updates.

   3. To compare (whether or not by use of automated tools on
   machine-readable files).

   See also vdiff, mod.

   [Jargon File]

   (1995-02-10)