What is a "MOD" and how does it differ from a "MOC"? In this imgur post, one of the images is captioned "MODs and MOCs - Ocean Beach, Kingsman Tailor shop, Sanctum Santorum."

If a "MOC" is a "My Own Creation," what is (the most commonly used definition of) a "MOD"?

This thread on Eurobrick suggests that "MOD" could stand for "My Own Design" (which might or might not be different from "MOC"), or could just be a relatively minor "MODification" of an existing set.

I didn't see a consensus over there, and I don't see the question raised on StackExchange yet, so I thought I'd ask StackExchange. What's a MOD? And when would you use that term instead of "MOC"?
It's MODification, "My Own Design" is silly.
Also used quite extensively outside of the LEGO community, e.g. in gaming a MOD is altered game code you execute, either to cheat or too change graphics for fun.

So an existing set where you altered things to is a MOD.

A MOC is created from scratch.