The term w00t is a slang interjection used to express happiness or excitement, usually over the Internet. The expression is most popular on USENET posts, multiplayer computer games (especially first person shooters), IRC chats, and instant messages, though use on the World Wide Web is by no means uncommon.
Usage of this term dates back to the mid-1990s, when it was probably derived from the alternative spellings of whoomp and whoot. These spellings are variously used in the phrases, "Whoomp, there it is," or "Whoot, there it is" from two songs in 1993 from rap groups Tag Team and 95 South, respectively. In those songs, the phrase is used exclusively for identifying voluptuous female buttocks. This is analogous to another derivation from urban African-American music scenes to mainstream, White American culture, namely rock and roll.
The definite origin of w00t is unknown. One theory claims it to come from the vocalization made by the player in games of the Quake series when a jump is performed; however, as Quake was only first released in 1996, this etymology probably only furthered the popularity of the existing term. Another derives from root, the traditional username for the administrator on a UNIX machine: it might be an abbreviation of "Woohoo! I just h4x0r3d [hacked] your box [computer] and got r00t!", or some such. Yet another theory is that w00t came from We Owned the Other Team.
Another possibility is that w00t comes from the sounds of jubilation by Daffy Duck.