1.A person who is interested in technology, especially computing and new media.
2.A person who has chosen concentration rather than conformity; one who pursues skill (especially technical skill) and imagination, not mainstream social acceptance.
3.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.
Geek is a more specific term. Back in the day, geeks worked at carnivals, and (according to the dictionary) “bit the heads off live chickens.” Thankfully, the term now has a different connotation. Like nerds, geeks are smart, but they tend to focus more on technology. As Urban Dictionary explains, these are the people you make fun of in high school and later work for as an adult.