Sometimes interchanged with geek, nerd, gamer, dufus and dweeb. Each have connotations that vary depending on who you talk to or the location. For example, nerd has a negative connotation on the eastern coast of Canada, while geek does on the west.
The definitions from my location are as follows:
A dork is someone that has less-than average intelligence, as well as having fringe interests like RPGs and computers.
A geek is someone who has a higher-than-average intelligence, and is interrested in a variety of fringe interests. The variety is unlikely to encompass the entire scope, and it is likely that the interrests will be interrelated. For instance, you might find a sci-fi geek, a history geek, or just someone who knows a lot of trivia. A geek will still have interests, friends and social skills outside of geekdom, though they may be more limited.
A nerd is someone who usually has a mich higher than average intelligence, but very poor social skills and very few if any friends and interests outside their area of expertise. They will usually have only one or two groups of interest, and are extremely passionate and knowledgeable about them. Often, a nerd will focus on numbers and definitions. A famous subgroup of nerds is the trekkies. There is usually a "mightier-than-thou" sentiment among nerds.
A gamer can be either a nerd, a dork or a geek, but their interests lie exclusively in computer, video and pen-and-paper games.
Dufuses and dweebs are generally regarded as clutzes and outcasts, without having the fringe interests or intelligence of either the geek or nerd groups. Sometimes dorks will fit in this category, too.
Here, only geek and gamer have a positive connotations, the rest are deemed insults.
Nerd: Jeremy of "Foxtrot"
Geek: Not as easy to find in comics, but anyone who reads sci-fi or fantasy novels is a good candidate.
Dork: Jon Arbuckle of "Garfield"
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