A geek is not a nerd.
A geek is obsessive over anything and everything: television shows (including Star Wars, Harry Potter and Doctor Who) it can be from comics, the internet and often consoles, pc games or related topics.
The geek will know everything about the given subject but despite this will have few problems socially.
However, in brief, a nerd applies to somebody who is a computer genius or enjoys maths,science or ICT to a large extent
Wow, John is such a geek all he ever talks about is Doctor Who!
I am such a nintendo geek- i have soo many of their games
Jill is not a geek- she's a nerd- she spends all her time on her computer