Noun

1. Shortened form of difference

   A peach and an apricot? What's the diff?

2. Any program which compares two files or sets of files and outputs a description of the differences between them.
3. The output of a diff program. A diff file.
   • 2004, Paul Graham, Great Hackers, Essay:

     I didn't want to waste people's time telling them things they already knew. It's more efficient just to give them the diffs.

4. Shortened form of difficult.
5. Shortened form of the profanity "dip fuck"

Verb

1. To run a diff program on (files or items).
2. To produce a description of changes made to a collection of files. To produce a patch file.
3. To compare two files or other objects, manually or otherwise.

Proper noun

1. A program, historically part of the Unix operating system, which compares two files or sets of files and outputs a description of the differences between them.