Taken again from wikipedia :)

A geek is a person who is fascinated, perhaps obsessively, by obscure or very specific areas of knowledge and imagination. "Geek" may not always have the same meaning as the term nerd (see nerd for a discussion of the disputed relation between the terms).

The definition of geek changed considerably over time. Below are some definitions of the word "geek"; all are still in use to varying degrees.

• A person who is interested in technology, especially computing and new media. Considered derogatory by some. Comparable with the classic definition of hacker. (Late 20th century and early 21st century.)

• A person with a devotion to something in a way that places him or her outside the mainstream. This could be due to the intensity, depth, or subject of their interest. This definition is very broad, and allows for mathematics geeks, band geeks, computer geeks, politics geeks, geography geeks, geeks of the natural sciences, music geeks, theatre geeks, history geeks, Good Eats geeks (Briners), linguistics geeks, sports geeks, figure skating geeks, SCA geeks (SCAdians), gaming geeks, typography geeks, ham radio geeks, public transit geeks (metrophiles), anime and manga geeks (otaku), Stargate geeks (Stargate SG-1/Atlantis fans, Gaters), Buffy the Vampire Slayer and Angel geeks, Star Wars geeks, Star Trek geeks (Trekkies and Trekkers, the latter noted for costuming), Tolkien or fantasy geeks (Tolkienite), and even Wikipedia geeks. (Late 20th century and early 21st century.)

• G.E.E.K., as an acronym, reputedly came from the United States Military; it stands for General Electrical Engineering Knowledge. It is unclear if this was the origin of the current meaning for geek, or if the acronym was used as a humorous reference toward the pre-established meaning for geek (i.e., a backronym).

• A derogatory term for one with low social skills, regardless of intelligence. (Late 20th century.)

• A person who swallows live animals, bugs, etc., as a form of entertainment at fairs etc. This often included biting off the heads of chickens. The Geek would usually perform in a "geek pit". This probably comes from the Scottish geck, meaning 'fool', in turn from Low German. (19th century.)

• The precursor word "geck" or "gecke" has been used in the works of Shakespeare: "Why have you suffer'd me to be imprison'd, kept in a dark house, visited by the priest, and made the most notorious geck and gull That e'er invention play'd on?" (Twelfth Night, V.i). The word also appears in Cymbeline.

Geek has always had negative connotations within society at large, where being described as a geek tends to be an insult. The term has recently become less condescending, or even a badge of honor, within particular fields and subcultures; this is particularly evident in the technical disciplines, where the term is now more of a compliment denoting extraordinary skill.