A 360 kickflip that is landed cleanly and stomped. A tre flip is a 360 pop-shuvit with a kickflip. See Mike-Mo's Fully Flared part on youtube for an example of a tre bomb. A tre bomb can also be a tre flip down a steep hill such as the ones in san francisco.
Dude! Bobby threw down a tre bomb the other day! or I beat Glen in a game of skate because i threw down the best tre bomb ever!