Hii

Float- It means you have been allotted a seat and you've accepted the seat but you want a better programme than what you've been allotted. In this case once you are allotted a seat in the further rounds, you'll lose the seat which was allotted previously. And the choices considered for float will be the ones which are above the allotted programme in your filled choices list. So its very important to fill choices intelligently. Focus on only those programmes which you want.

All the best.