All of the definitions above. Someone who vents their bitterness on Urban Dictionary like a passive-aggressive wimp because they were always chosen last in gym class.
They have a few false beliefs, such as convincing themselves that they are geniuses (watching anime doesn't make you a genius. John Nash was a genius.) and that their social ineptitude is other people's fault. They use the old "I will be more successful" mantras like it isn't an obvious defense mechanism, and is a very broad assertion that isn't true.
A nerd is an interesting sort of idea. To some, the idea comes simply: glasses, nasal, scratchy voice. Inhalers, pocket protectors. Whatever the hell.
I think a nerd is something else. Someone who has a large IQ, sure. But doesn't act that way. A nerd is a person who plays video games, spend their money on new releases and Trading Card Games. Ones who, online, are actually, well, literate. A nerd can be extremely annoying or really cool. Depending on your point of view. And hey, since they have a non existant life, they have all the time to talk to you. One more thing: Nerds like to trash talk a lot of things behind your backs. Rap, emo, goths.. Whatever is around the bend.
Face it. Nerds whoopyour butt. Not only are they smart, but they can have you on your butt crying when it comes to the infamous XBox queen. Halo.
The people responsible for all the awesome shit we have (the internet, for example). Also the people responsible for bringing us the best movies, TV shows, books, video games, and the list goes on...
The Simpsons (in its heyday), Futurama, South Park, The Mario, Donkey Kong and Zelda franchise of video games, and the ability to communicate with anyone in the entire world in a fraction of a second are just some of the awesome things we can attribute to nerds.