From The Free On-line Dictionary of Computing (8 July 2008) [foldoc]:
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)
From Jargon File (4.4.4, 14 Aug 2003) [jargon]:
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.