Quiz: Remember the definition of mal de mer?
Difference: What's the diff? (mid-1800s+)
/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!"
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.