If you could be more specific as to in what context you are asking this. We could have helped you better.
Open house counselling cum admission
This is one of the final rounds of NSIT. If you have ever attended COMED-K counseling, they have an open hall with a display of seat matrix. Candidates are called as per their rank and they exactly know the vacant seats.
One of the final rounds of CCB, where you directly report to the allotted institute and get admission.
Normal counselling procedure, where candidate has to be physically present for the counseling process as in case of final round of PEC or Thapar University