And to expand on Big T's answer- geek is a negative term. It's an insult.

The definition of Geek has changed a lot over time and does not necessarily have a negative meaning. One definition reads this way, "A person who has chosen concentration rather than conformity; one who passionately pursues skill (especially technical skill) and imagination, not mainstream social acceptance." This definition is the closest to the current common usage. I do not consider the term to be an insult. Many people, including myself, take it as a compliment. There is a computer repair company called Geek Squad which is a highly respected nationwide firm. In the technical disciplines, the term is now often a compliment, denoting extraordinary skill. If someone calls you a computer geek, then that means that you know everything about computers and their operation. Geek chic is a fashion trend that resulted from glamorization of "geek culture" in the 2000s decade, such as the use of computers, video game culture, the Internet, anime, Superhero films, fantasy novels, along with the high income of so-called "geeky" jobs such as Information Technology. You should be so lucky as to be called an English Geek! Sorry I didn't get to answer you better during our chat, I was very busy at the moment. I hope this answers your question.

A geek is someone who knows everything. Another work for geek, is nerd. An example might be: "Waldo is such a geek, he memorized the whole encyclopedia!"