Q:

What is float-cancelling?

In Super Smash Brothers Mêlée (SSBM), Princess Toadstool (Peach) is a playable character. She has the ability to float as a function of holding a jump button (X or Y). There seems to be an advanced technique involving performing aerial moves while floating, similar to L-cancelling. 
What is float-cancelling? 

A:

Float-cancelling is a technique/exploit/glitch/bug/etc where, if Peach is floating when she uses an aerial attack, she does not go through the attack's landing lag if she hits the ground during the attack. Generally this is done by floating into an incline to land. Since normal landings are even faster than L-cancelled landings, this basically lets the player do things faster.

