1. When posting on a forum, you submit a post only to find that someone has posted the same thing only seconds earlier.

2. When someone gives another person such a good comeback that the person being exposed to the torment never even sees it coming. But the burn does not end there my amigos. The Ninja'er comes back for a second attack, ending with their battle cry, "Ninja'd!" Then disappears before you even have time to pee your pants from shock. Here's a diaper baby, clean yo'self up. You be dirtying up my new kitchen floors. .. bitch.

3. In chat, it is the act of saying something before someone else. It only counts if someone else actually says the same thing afterwards.

4. the act of stealing, swooping, or snaking something. the person who has been ninja'd upon does not realize it for a little while.

5. A new tactic the the FPS Xbox 360 game, Halo 3. A Player lures another player into following them. Player 2 is following player 1. Player 1 goes around a corner. Player 2 Follows. Player 1 jumps backwards, and Player 2 passes under Player 1. Player 1 Melee's Player 2 and instantly dies due to an assassination. Ergo, Ninja'd.

6. When someone takes something or someone away from you and you did not know whats the fuck is going on until the person ninja'ding you is laughing his/her/ ass off. The term ninja'd is usually mixed up with thiefed but the stupid sob that did that is spread across the atlantic ocean....Right now.