If you are single and in NYC, you may have a roommate and there may be a time when you both do not get along. Assuming you are the only party on the lease, a roommate holdover case is brought to make a roommate leave the apartment or house that you share. You cannot lock your roommate out of the home you share without a court order.
For more information, see
http://nycourts.gov/courts/nyc/housing/holdover_roommate.shtml