The word geek is a slang term, with different meanings ranging from “a computer expert or enthusiast” to “a carnival performer who performs sensationally morbid or disgusting acts”, with a general pejorative meaning of “a peculiar or otherwise dislikable person, esp[ecially] one who is perceived to be overly intellectual”.
This word comes from English dialect geek, geck: fool, freak; from Low German geck, from Middle Low German. The root geck still survives in Dutch and Afrikaans gek: crazy, as well as some German dialects, and in the Alsatian word Gickeleshut: geek’s hat, used in carnivals.
The word appears in the modern sense of a science, math, or technology enthusiast in Robert Heinlein’s 1952 short story “The Year of the Jackpot”.
Formerly, in 18th century Austria-Hungary, Gecken were freaks shown by some circuses. In 19th century, in North-America, the term geek referred to a freak in circus side-shows. In some cases, its performance included biting the head off a live chicken. The 1976 edition of the American Heritage Dictionary included only the definition regarding geek shows.
Although often considered as a pejorative, the term is also often used self-referentially without malice or as a source of pride – an example is the ‘Geek Squad’ of the Best Buy company.