A front butt, usually found on fat people. When a person's stomach/genital area sticks out as far/further than their butt.
*while some dudes were at a water park*
Dude 1: duuuude what is that?!?!
Dude 2: WHAT HUH WHAT?!?!
Dude 3: dudes that's a futt. now get over it and stop looking at fat girls.