Someone who aspires to be a dork or geek, but fails. While a dork is funny and clever, and a geek is smart and computer savvy, a nerd who attempts to be a dork ends up being annoying and when attempting to be a geek ends up being stupid. A nerd is a wannabe dork/geek.
"Hey, Mr. Geek, did you see that nerd? He was copying you, only doing a crappy job of doing so!"
"Yeah, I saw him, he was following that dork around, telling him dumb jokes and pissing him off."