What is an a-b in wholesaling?

[Caito Coloma]

I am in the middle of buying my first investment property from a wholesaler. I have purchased properties before but never through a wholesaler. They sent me a message saying that the assignment contract was going to be sent over and once I sign he will be sending over the a-b. Does anyone know what that is or what it means? 

Any feedback is appreciated.

Thank You