A person who's highly intelligent and generally is against the mainstream of society. Unlike the goths, they are truely non-conformists. In the past they were generally shunned by society due to a lack of physical attractiveness, intelligence, and unusual maturity. A great illustration of Nerd life "back in the day" is the Revenge of the Nerds movies. In the modern area a "nerd" no longer is shunned from society. A modern nerd generally likes computers and video games. They could look like the nerds of old but they can also look like normal people.
Many have theorized to why nerds have been accepted into the mainstream. Two popular theories is that when video games became mainstream nerds and their mortal enemies the jocks were able to become friends. Also because computers now dominate our society nerds are accepted.
Also take note that the portion of nerds who are still shunned from society have became either a goth or an emo.

One whose IQ exceeds his weight.

An individual persecuted for his superior skills or intellect, most often by people who fear and envy him.

An 'individual', i.e. a person who does not conform to society's beliefs that all people should follow trends and do what their peers do. Often highly intelligent but socially rejected because of their obesssion with a given subject, usually computers. Unfortunately, nerds seem to have problems breeding, to the detriment of mankind as a whole.

A stereotypical label used to describe a person that is socially inadequate. A four letter word, but a six figure income.

A person who gains pleasure from amassing large quantities of knowledge about subjects often too detailed or complicated for most other people to be bothered with.

Often mistaken for Geeks, who aspire to become nerds, yet lack the intelligence, and end up giving nerds a bad name due to their poor social skills.

Non-nerds are often scared of nerds, due to their detailed knowledge, and therefore seemingly high levels of intelligence - and subsequently denegrate them as much as possible as often as possible.

Nerds exist covertly within the fabric of society, often choosing to 'nerd it up' in private or in the company of fellow nerds. It is for this reason they are feared the most - unlike geeks, who are easily identified, nerds can only be found out when casual conversation reaches a subject that they like nerding.

Never
Ending
Radical
Dude.

the group of people who will most likely make a life changing invention that will radically change the world. the computer was invented by a nerd. the macintosh/apple and windows were invetned by nerds. jocks and normal people have no claim to civilization except for being the hard labor. nerds actually do the thinking. so jocks, fuck you, and go eat your steroids