Hii aspirant..

First of all I would I like to tell you about what is the concept of spot actually. In the spot round of counselling a student is said to do physical reporting at the reporting centre as been decided by the exam conducting board. And then in this process the seats which are vacant that is the seats which are left after the rounds of counselling are being filled by allotting them to the students who did not get their Desired seats get in the desired college.

Generally this processes officially being used by the government colleges to fill the vacant seats that are being left after the completion of counselling process.

But this round is conducted for private colleges as well the conditions differ from college to college. Where as some colleges conduct there spot counselling themselves by providing the paid seats to the students.

Hope it helps. 

Best of luck.