Out Of Character. A term used in roleplay when a person wants to step outside of their character for a minute and speak as themselves.
OOC is shown in a couple of ways, commonly with a label or as double brackets.
((Can I say something for a sec?))
or
OOC: Can I say something for a sec?
OOC's antonym is IC, or BIC – “In Character” or “Back In Character.”
Source: Urban Dictionary