Fen

A fen is a type of wetland fed by groundwater and runoff, and containing peat below the waterline. It is, in many ways, intermediate between a bog and a marsh. Fen is an Old English word considered to have proto-Germanic origins, since it has cognates in Gothic, Old Frisian, Dutch and German.

See also the English district of East Anglia called The Fens.

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Fen is an invented alternate plural of fan, and is used by science fiction, fantasy, and anime enthusiasts to distinguish themselves from "fans" such as football fans.