Yes,  i understand your query regarding this as i would like to give you a brief about this as follows :

The Mop Up round is the process of counselling of seat allotment in medical colleges by states against the reverted seats from All India 15% qouta. This round is only for those candidates which do not get seats in round 1 and round 2. This is not applicable for the candidates who already got seats alloted. Candidates who are qualified but do not get any seat in round 1 and round 2 they are automatically eligible for Mop Up round. You have to fill separate form for this round. The dates will display at the time of counselling. 

It is a chance to get a seat in government college irrespective of lower marks than state cut off. 

Hope this helps. All the best!!