Other forms: otakus
If you've got an eccentric friend who enjoys some unusual hobbies, you may already know an otaku, a person who is obsessed with a very specific subject or with pop culture.
Otaku, mainly used in Japanese, has an unusual origin: It comes from the historically very formal Japanese words meaning "your house." Young people with specialized interests in things like anime, video games, and manga would use this pronoun as a very polite way of addressing and recognizing each other. Outsiders noticed, and the media remarked on it, so it became a general term for these young people.