1) A person who is new to a game
2) A person who, regardless of experience, lacks the skill or copmetence to be competitive in a certain game
3) Someone who tends to whine or complain when being beaten at a game - often done by accussing more skilled opponents of hacking
4) One who may talk trash, claiming to be elite at a game, only to be beaten down by a better player, or will turn down any games when challenged by better players.
1) To act or behave in the way that a n00b would
2) Behaving as if lacking experience, skill or knowledge
NOTE: Can be used with a number of connotations. Often is used mockingly or in a manner of jesting. Other times is used seriously, but is often considered a brainless or weak insult when used alone as a supposed malicious insult. Is generally considered rude and deragatory unless a person is displaying disregard and general apathy towards other players - in this case, skill may be a non-factor (see definitions 3 and 4).
See also n00bed
, and newbie