Fusion is a technique which the Z Warriors learn in order to try to stop Buu. When some one fuses their speed and strenght increase dramaticly.

The first fusion that was performed was between Piccolo Nail. This fusion is called "Namek Fusion".When Nail and piccolo fuse Piccolo absorbs Nail,but doesn't change his appearence.

Second fusion performed was the Fusion Dance.This fusion is performed by Goten and Trunks.In order for this fusion to work they have to have the same poer level and do the dance percicely.When the performe this dance their bodies fuse and produce and new body much stronger and faster.

The third fusion is with the earrings that the Elder Kai gives Goku.To perform this fusion one person has to put an earring on one ear and the other person on the other.

Piccolo + Nail = Piccolo (Namek Fusion)
Goten + Gohan = Gotenks (Fusion Dance)
Goku + Vegeta = Vegetto (Earring Fusion)
Goku + Vegeta = Gogeta (Fusion Dance)