MY definitions:
Nerd: someone who has a weird obsession with something
-Video game nerd: someone who likes, one of the following and rarely plays anything else: a specific series, a specific genera, or a specific company
-sub categories: MMO nerd, cosplayer, stuff like that
Geek: someone who knows to much about a certain subject
-Computer geek: the type of people that made the computer you have, as well as your precious phone and ipod. also called computer nerd
-Basement Geek: does this really need an explanation? if you are over 20 and live in your moms basement either making websites with pictures of various things or playing wow, or something like that, you are a basement geek or basement nerd, or guy who lives in his mom's basement.
-misc. Geek: stereotypical nerd, always picked on at school, not very many friends, but usually good ones.
Dork: a whale's penis (i did not make that up)
Nerddork: someone who does very well in school, and does there best. i don't expect many people to have heard that term before, but if you have, let me know.
these are NOT concrete definitions, and you only have to have a couple of the characteristics mentioned
nerds and gamers are NOT the same
there are also other subcategories