Geek originally referred to a performer in a circus sideshow who engaged in bizarre acts like biting the heads off live chickens.
In modern usage, geek describes someone who is extremely knowledgeable and passionate about a particular subject, especially technology, computers, or science fiction.
The term "geek" also refers to:
1. A person with a high level of expertise in a technical field
2. Someone who is socially awkward but brilliant in their area of interest
3. A subculture that celebrates intellectual pursuits and niche interests