Nerds vs. Geeks
Nerd is frequently used as a derogatory term, but has rather aggressively been reclaimed by self proclaimed nerds, among them Mayim Bialik, who plays the supremely nerdish Amy Farrah Fowler on The Big Bang Theory, who just happens to have a real-life PhD in neurobiology, and who proudly proclaimed herself a nerd in high school (when she had already been a TV star). Dr. Seuss seems to have been the first to use the word in print, but it had no obvious referent except as one of the exotic creatures Gerald McGrew intended to collect for his zoo.
It thereafter seems to have acquired its sense among teenagers as a socially awkward person, especially one of an intellectual bent. Nerd reclamation turned the insult into a compliment as a synonym for intelligent or intellectual, although the connotation of social awkwardness has never disappeared. Today, if you have a degree or occupation in a STEM field you are more or less a nerd by default.
Geek, another insult that has been partially reclaimed, originally referred to the kind of carnival performers who bit the heads off of live chickens. It's frequently applied to those in the computer field, usually in a somewhat disparaging way: "My computer won't turn on. I will have to call the IT geek."
Bialik, in a discussion with Stephen Colbert on his show, had her own taxonomy. She, by virtue of her neurobiology PhD and interests, was a nerd. Colbert suggested that he too was a nerd, based on his encyclopaedic knowledge of all thing Lord of the Rings. No, corrected Bialik, you aren't a nerd, you are a geek. Membership in Kingdom Nerd, it seems, is reserved for those who study scientific subjects. Of course I haven't seen her on Colbert since.
In that system, the male scientists of The Big Bang Theory are both nerds and geeks. Besides being science nerds (at Caltech, the Rome, Mecca, and Jerusalem of nerd-dom), they are comic book geeks, Star Trek geeks, video game geeks, etc. That's probably unusual in real life as both geeks and nerd tend to specialize*, but science just isn't quite funny enough.
*Full disclosure, I know, or at least used to know, a heck of a lot about both the Lord of the Rings and Harry Potter.