An OC Stand In is a term for when an author uses an existing Canon Character that gets little screentime or few (if any) lines, and therefore can be molded into whoever the fans want or whatever is necessary for the story. They may sometimes be background characters or involve extrapolating ideas from a brief on-screen appearance. OC Stand Ins can be like original characters, but they come pre-packaged with at least some minor characteristics, giving the author some general direction to go in.