Hey Yash

It means that no one filled the choice for that branch and the students who get the seat also do not change their branch or college. Or it may be possible that all the seats have been filled in previous round.
Like if there are 100 seats in 5 the round and all the seats occupied by students and in 6 the round no one change their branch from those 100 students than in this case opening and closing rank remains same.