A newbie or newb to me is just someone who's new to the game. A "noob" is...
A middle school blood elf hunter who spouts memes like they're the most hilarious things ever invented, proclaims even small errors as "EPIC FAIL", then asks for a battle rez, more mage food, and probably a repair bot when they don't move out of the way of the slime during that one fight in Naxxramas because they're too busy scrolling through iTunes for an appropriate Metallica track. The kid whose voice makes you want to stab yourself in the ears with an icepick, mostly because he has no volume control on his vocal cords and because his balls haven't dropped. He's the kid who's been playing for almost a year and still finds ways to cock things up as if he only started playing yesterday. Likely takes Ritalin or something along those lines, has the attention span of a puppy surrounded by beef jerky, completely rude to his fellows...
I had to deal with one of these yesterday, so excuse me if I seem annoyed. There are more types of noobs but these are the most irritating kind.