I assume the meaning of the name is a short way to say procedure,
much like of int in other OOP languages is shorthand for integer.
I ask this because the Ruby document site didn't addressed it in it's Proc page.
The Ruby Language Reference Manual (1998 by Yukihiro Matsumoto) refers to it as “procedure object”:
The
Procis the procedure object, which is the encapsulated block with context, such as local variables and stack frames.