I always thought "noob" meant someone who is pretty bad, typically who has just began
"Noob" comes from the word "newbie", the latter word meaning a player who is new to the game. When people would use the word newbie, it was more as a description to indicate a lack of familiarity. When people began to use the word "noob" for short (sometimes used to be spelled "newb"), it took on a connotation of sucking. Everyone always realized new players often sucked due to a lack of familiarity, but using the word "newbie" emphasized that this was a new player who needed guidance and help to learn the game, whereas using the word "noob" emphasized that this was a new player who sucked and who should be dominated.
Because the emphasis of the word "noob" is the lack of skill associated with a player, gamers started calling anybody who sucked a "noob", whether or not they technically were new to the game, and the word has somewhat taken on this meaning. Often times, you have no idea how experienced your opponent online is. And if you beat up on an opponent really bad in a game, you can call them a "noob" without worrying about their actual experience, because if they respond "I'm not a noob, I've been playing this for years" you have multiple comebacks at your disposal...
"Could have fooled me..."
"Well you sure play like one."
"You've been playing for X years and you're still this bad?!?"
etc, etc, etc....
So nowadays "noob" emphasizes that a player sucks first and foremost, but should also, technically, include that a player is new. A player who is a veteran but who sucks is simply a player who sucks.
~17 years of gaming experience (probably more years than Bubbles total age)