User blog comment:LongClawTiger/Big Collab Idea with main cast of SI OCs!!!/@comment-3337043-20110219000909/@comment-2045351-20110219001913

OC (Original Character) is any of your characters you create for various purposes. SI (Self-Insertion) is usually a single character that represents you, and often do most if not all the same things you do, and best represent you.

All SIs are OCs, but not all OCs are SIs