A fan or fanatic, sometimes also termed an aficionado or enthusiast, is a person who exhibits strong interest or admiration for something or somebody, such as a celebrity, a sport, a sports team, a genre, a politician, a book, a movie, a video game or an entertainer. Collectively, the fans of a particular object or person constitute its fanbase or fandom. They may show their enthusiasm in a variety of ways, such as by promoting the object of their interest, being members of a related fan club, holding or participating in fan conventions or writing fan mail. They may also engage in creative activities such as creating fanzines, writing fan fiction, making memes or drawing fan art.

A fandom is a subculture composed of fans characterized by a feeling of camaraderie with others who share a common interest. Fans typically are interested in even minor details of the objects of their fandom and spend a significant portion of their time and energy involved with their interest, often as a part of a social network with particular practices, differentiating fandom-affiliated people from those with only a casual interest.