Hello Sridarsini

BC means backward classes while OBC means other backward classes. We often see that in counselling process we came to know OBC is written as Simply BC. So You don't have to worry regarding such short term, they generally avoid O because either for typing purpose or because of the fact that BC itself means backward classes includes all the classes which are backward. So both are same thing.

Good luck :)

Feel free to ask if you have any further queries.