Mod is a wonderful but never used command that came with 2.35. Whereas div takes the quotient, mod takes the remainder.
Ie: mod = modulos command. 5 6 mod is 5. 6 5 mod is 1. (5/6 = 0 remainder 5. 6/5 = 1 remainder 1).
There are a few other never used commands as well. pyth being an example (would be useful in complex vector manipulations.)
They're all listed in the readme for 2.35, as well as how they work.