My understanding would be that a donk bet is when villain bets out after just calling a pre-flop raise OOP. Usually, play would be checked to the pre-flop aggressor.

Reverse float, in my opinion, sounds like it could be when you're the pre-flop aggressor and you c/c the flop having not connected with it. For example, you 3bet from the BB against BU w/ AKs, flop comes 963r and you c/c. I think this would classify as a reverse-float.