there are two types of counsellling. First done by DGHS for 15 per cent all India quota seats and deemed and central universities; and second done by individual states through state counselling auhtorities. Both kind of counselling is conducted into two rounds. after two rounds, if the seats are still vacant then the counselling authorities organise mop-up rounds to fill the vacant seats. For this, candidates are made to do fresh choice selection.

hope this will help.

best of luck.