It means original character, या प्रशंसक character. People create them for fantoms and such. I have a हेतालिया one, Oregon, along with a bunch of people from our RP.
OC= Original Character I have a few, one of them that will probably never see that fanfiction world (I do not प्रकाशित करे my Sopranos fics) is Sonia Moltisanti...the और level headed twin sister of mafia man Christopher Moltisanti. (TMI I know)