The oh so reputable wikipedia defines nerd as: “Nerd is a term often bearing a derogatory connotation or stereotype, that refers to a person who passionately pursues intellectual activities, esoteric knowledge, or other obscure interests that are age-inappropriate rather than engaging in more social or popular activities.”
That usually conjures up the image of something like this:

I would disagree with wikipedia on the issue of age-inappropriate, since this assumes that all nerds are into video games, or trading cards.
I would define nerd as anyone who had a passion or interest for any specific thing. One can easily be a video game nerd just as easily as a car nerd, or a basketball nerd. As long as you love something and research it.
I would argue that these “nerds” are the only people who are actually alive, the only ones who actually matter. The exact opposite of the nerd is the conformist. I don’t mean to sound highschoolish about this. The conformist to me is the person who is jack of all trades, master of none when it comes to hobbies. These people can easily be identified on myspace of facebook. They usually list a lot of generic interests, without overly emphasizing any of them.
These people like a couple of mainstream bands, but aren’t overly into any of them, they don’t analyze the music, or anything. They usually list some generic mainstream sports, like basketball or football, might like a particular team, but don’t really care much beyond that.
Now I don’t overly like sports, but I can respect a sports nerd. Someone who is very passionate about a game, someone who analyzes teams, plays, and players. They have a passion. Those conformists, they’re just mindless sheep that float through life, going with the flow, blending in with whatever is popular. They’re a dime a dozen. Not saying they’re worthless people, they’re still human beings, but they’re not interesting. There is nothing unique or special about them.





Funny, when I read “age-inappropriate” my first thought was young kids being into mature interests way above what one associates with kids their age. A positive thing. But you’re right, it was probably meant as a negative “look, they haven’t outgrown that yet” thing. Which in itself is a problem, since who defines these things?
I think that wikipedia definition might have read better if it instead discerned that “nerd” activities tend to go beyond the intellectual capability of the general population. It is taxing and very sad that under these given conditions and connotations our culture and this wikipedia author felt that one’s intellect should only be used at certain ages and must make emphasis to point out that specialties are “abnormal”. Yeah, keep those kids away from what they’re predisposed or geniuses at, it’ll get them far in life, social liegeislators.