first of i would like to clear some things up. people have been defining this word as someone who is inexperienced and new to the game, This is close but incorrect.
The actual definition of noob is someone who has been doing something for awhile but is still really bad at what ever that may be.
pro: man are you a newb?
noob: nah ive been playing for 6 months
pro: OMFG ur such a fukn noob ur so shit!