geek
A person who is very passionate and knowledgeable about something.
A geek is someone who is deeply passionate and knowledgeable about a particular subject, often something technical or specialized.
Today, being a geek usually means diving deep into something you love. A computer geek might spend hours learning programming languages or building custom computers. A science geek eagerly reads about black holes and quantum physics. A theater geek knows every musical by heart and can quote Shakespeare from memory. The key isn't what you're interested in, but how enthusiastically and thoroughly you pursue that interest.
The word suggests someone who goes beyond casual interest. While someone might enjoy playing video games, a gaming geek studies game design, speedrunning strategies, and the history of different consoles. A history geek doesn't just learn names and dates for tests, but reads original documents and debates different interpretations of historical events.
Geek is often used interchangeably with nerd, though some people make distinctions. Generally, geeks are thought to focus on specific hobbies or fandoms (comic book geeks, space geeks), while nerds lean more toward academic subjects. But the overlap is huge, and most people use the words to mean roughly the same thing: someone who embraces their intense interests without apology.