Out Of Character (OOC) means someone is speaking as themselves, and not in a fictional sense. (OOC) is used as a prefix to any thing not meant to be In-Character, usually referring to rules or information that they wish to either tell or discover.
Example: A random member posts the following in a Run-On on the Forums:
The Dark Jedi draws his saber and lunges at his
opponent, slashing quickly downward has he falls.
(OOC) How many posts do we get for this battle?
Can my lightsaber be a normal one yet or do I
still have a training one?