1. See newbie.
2. A person that never googles, no matter how many times you tell them to, but instead persists on spamming you senseless with questions they could easily get the answers to themselves.
3. LoneShark (<3)
I believe the word derives from the Natural Selection gaming community (try typing "fu noobcake" when skulks are eating you). It's commonly used to express frustration when dealing with someone's lack of knowledge within a certain area of expertise. Heh, that's probably the nicest way I could put "badmouthing nooblets who should be banned from using computers".
omg... STFU NOOBCAEK.