The word geek is a slang term originally used to describe eccentric or non-mainstream people; in current use, the word typically connotes an expert or enthusiast or a person obsessed with a hobby or intellectual pursuit, with a general pejorative meaning of a "peculiar person, especially one who is perceived to be overly intellectual, unfashionable, or socially awkward".
Although often considered as a pejorative, the term is also used self-referentially without malice or as a source of pride. Its meaning has evolved to refer to "someone who is interested in a subject (usually intellectual or complex) for its own sake".
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From @gomo