Nowadays the word geek is a slang term originally used to describe odd or non-mainstream people, with different connotations ranging from "an expert or enthusiast" to "a person heavily interested in a hobby", with a general pejorative meaning of "a peculiar or otherwise socially inept person, especially one who is perceived to be overly intellectual".
Although often considered as a pejorative, the term is also often used self-referentially without malice or as a source of pride. Its meaning has evolved to connote "someone who is interested in a subject (usually intellectual or complex) for its own sake."
But in the early 20th Century a geek was a circus freak and geekery meant bizarre physical acts performed by geeks. Amongst these were carnival performers, often billed as wild men, whose act usually included biting the head off a live chicken or snake. Gross!
The meaning changed to its more expert / eccentric one after Robert Heinlein used the term geek to mean a maths freak in 1952.