There are actually several different types of the species nerd. "Nerd" is a very broad term, and there are different shades of nerdiness. We are not geeks. A geek is a circus performer who bites the heads off live chickens. Look it up. I have identified in pop culture several distinct types of nerds, which I will attempt to describe here.
The Classic Nerd
The classic nerd existed before the modern computer age. He is the stereotypical nerd, usually male, with horrid fashion sense. He pays no attention to his clothes, is obsessed with technology, and sees the obvious benefits of a pocket protector. Almost always wears glasses, probably has a funny sounding voice. Lacks all social skills, and is a fountain of useless knowledge. The Classic Nerd is more a media creation than anything else, you rarely see the type in real life, although they do pop up occasionally. Malcolm in the Middle has some great Classic Nerds.
The Computer
Nerd
A common occurence in the modern computer age, the Computer Nerd is obsessed with computers. Again, usually male, he shares a lot of qualities with the Classic Nerd including the lack of fashion sense and social skills. Of course, there are some cool computer nerds out there. This is just an extreme form. This nerd knows the computer inside and out, has a room full of what appears to be spaceship parts. He obsessively plays computer games, sometimes to the exclusion of all other activities. He is frequently caffeine dependent, and may hang around with other computer nerds, or just have online friends.
The Smart Nerd
This is definetely the type of nerd portrayed in this comic, and is possibly as prevelent as the Computer Nerd. The Smart Nerd can go undetected and hide in crowds. They are defined by their high IQ, wealth of useless knowledge, and strange hobbies. Reading is probably the biggest hobby for most of these nerds, usually science fiction and fantasy, but they have a general thirst for knowledge that leads to very interesting reading. This results in a high vocabulary and lack of social skills and probably motor skills, since who wants to go play soccer or kickball when you could read "A Wrinkle In Time?" Smart Nerds can accel in a particular field, usually scientific or mathematic, and are also defined by their high grades. Smart Nerds are often lonely, since they seem to average about 1 per elementary school class. Eventually they find other Smart Nerds and become really interesting people. Until then, they are frequently labeled as teachers' pets.
There are, of course, many different shades of these nerds, and probably some I've left out, but I'm defining a nerd as being very smart and/or having expertise in a particular field, as well as being socially inept. That pretty much excludes class clowns, goths, and many other people who are "socially different." These nerd-types can also overlap. Remember, these are the extreme forms. Of course, I've also just spent 45 minutes classifying nerds. Which probably makes me a nerd. But I already knew that. That's why I have a comic.