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!"
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.