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.