Out Of Character
Out Of Character is a term used in role playing games, and is used to mean that a player is speaking as the real life player instead of the character they are playing, as opposed to In Character. Some games require players to make it obvious when they're talking out of character, for example by prefixing the sentence with "(OOC)". Some MUCKs provide this functionality in their say and pose programs.
It can also mean actions inconsistent with the established behavior for a character. For example, a wizard suddenly taking a sword and running into battle would be out of character in most settings.