What are mock allotment and is there any relationship between it and counseling

mock allotment is a procedure of providing seats to those who have qualified competitive examinations after the counselling. For example -

JoSAA 2018 is the mock allotment where they allot seats for those qualifying JEE mains or JEE advanced in 2018

This allows you to get an idea about the seats in a course you might get based on your preferences. What they do is, they see the number of people who have earlier filled the same preferences and then provide you an idea of what seat you might get in case the people do not change their preferences. You can then change your seat if you do not get the desired one.

Usually the seat you obtain is around the one you were allocated on the mock allotment. It might just go higher or lower a bit.

I hope this helped.

All the best!!