To get lucky. To win in a contest based on luck or cheats. The first use of this word originated from the character "Noob Saibot" in the video game "Mortal Kombat II".
The character Noob Saibot was named after Tobias Boon (Noob Saibot spelled backwards), one of the creators of the game. Considered to be the most dificult character of the game, Noob Saibot would "cheat" to win. Some would say their defeat by Noob Saibot was luck, chance.
It was common to hear someone say "you got noobed" when they would unfairly lose or to be called a noob if the person won in a "cheating" or "lucky" fashion while playing in a video game arcade.
Example 1 for Noob (2nd Definition) -
Person 1: Wow, that guy was lucky!
Person 2: Yeah, you got noobed!