The plural, genderless form of "fan", for when 'Fans' just won't cut it. This is fan jargon, formed by a tongue-in-cheek analogy to the pluralization of "man" as "men".
Certain aspects of fandom, especially early SF fandom, preferred this term to "fans," hoping to distinguish from, for example, sports fans.
Also, and perhaps not coincidentally, a synonym for "swamp".
- In an episode of Crusade, a race called the "Fenn" is discovered to live in hyperspace. One character describes them as "harmless, and attracted by shiny objects." Knowing J. Michael Straczynski, it's got to be deliberate.
- The fiction community Fenspace is named after this trope.
- The origin of the slang term Fench - Fen Stench. It specifically refers to the odor of any large fantasy or sci-fi con towards the latter half, as many fen decide they don't need to sleep during the con - or shower, either.