The Fandom reference article from the English Wikipedia on 24-Apr-2004
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Fandom

Keen aficionados of any phenomenon such as authors, ideologies or fashions (fans) can collectively manifest as fandom. Fanss typically are interested in even minor details of the object of their fandom; this is what differentiates them from those with only casual interest. The objects of fandom are typically artistic, sporting or entertainment related. For example, it would not be usual to refer to an accountant who is really interested in the details of accounting to be a "fan" of accounting.

A term for a member of fandom is "fanboy".

See also: Science fiction fandom, Furry fandom

The term fandom is particularly associated with fans of the Science fiction and Fantasy genres, who originally coined the term (a portmanteau of "fan + (king)dom".