Basically, anyone who's into ANYTHING besides testosterone fueled recreational or professional activities, IE, sports
music, drinking or street racing
. If it's an intellectual interest, one that requires more than a 3rd grade education to understand, you can bet that it has geek followers.
Yo man, who's dat geek ovah dere, he don't dress like a hiphoppa, drive a hoop, play hoops or drink as much beer as us, must be a geek.