Hello Rajasekaran Umamaheswari

Mock Seat Allocation is a procedure to appoint Seats to Students who qualify Completive exams after Counselling.
For ex:- JoSAA Counselling 
It is Seat Allocation procedure for those who have qualified the JEE Main or JEE Advance. The main purpose of this collaboration is to provide a common platform to all the engineering aspirants to apply to India’s best engineering colleges or institutes.

Hope this will be helpful

Good Luck.