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!
Tre: derived from the french word tres meaning (and substituted for) the word 'very'. Except, in this context it is written phonetically and you leave out the s. (The irony makes it hip)
Book: derived from t9 predictive texting. When attempting to type the word 'cool' but t9 recognizes it as 'book'. People got lazy (people in Davis, Ca, to be exact) and left it as is, substituting 'book' for 'cool' in texts. trend eventually spread to spoken word.
-Often (but not exclusively) used sarcastically when apathetically humoring another person, but really the person doesn't give a shit.