Talk:Orihime/@comment-84.220.160.29-20130902092153/@comment-49.144.240.189-20130903024425

Proc is an abbreviation of the word procedure, a term used regularly in the world of programming. A procedure (subroutine, event, method) is simply a block of code that carries out a specific function and is triggered under special circumstances.

It's not hard how to imagine how it might have entered common speech from there. You know, developers and players talking with each other. Or developers as players themselves casually using it often enough that people around them get it, even if they're not programmers themselves.