a single-minded expert in a particular technical field.
"a computer nerd"
'Contemptible' seems a little harsh - not that Mr Zuckerberg will be crying himself to sleep over it.
Where does the word come from?
For the origin we are indebted (again) to the magnificent Dr Seuss
The first documented appearance of the word "nerd" is as the name of a creature in Dr. Seuss's book If I Ran the Zoo (1950), in which the narrator Gerald McGrew claims that he would collect "a Nerkle, a Nerd, and a Seersucker too" for his imaginary zoo. The slang meaning of the term dates back to 1951, when Newsweek magazine reported on its popular use as a synonym for "drip" or "square" in Detroit, Michigan. By the early 1960s, usage of the term had spread throughout the United States, and even as far as Scotland.[9
Usage increased steadily throughout the 60s - with Sci-Fi writer - and uber-nerd - Phillip K Dick, even claiming to invent a new spelling ('nurd'). But nerd entered the mainstream by frequent appearances in the popular comedy series about 1950s family life, Happy Days. It's doubtful that this was historically accurate but nor were there too many forty-something leather clad bikers in the average suburban household either...
What is the difference between a nerd and a geek?
And a hipster?
A hipster might happily endorse the 'contemptible' label for nerds. But an aspiring hipster can look pretty nerdish to the untrained eye .....