Het
Definition
Het is an acronym for Heterosexual and means any kind of fic that includes or evolves around a heterosexual relationship. Mostly, het fic is romance fan fiction with the focus on a relationship between a man and a woman.
The Supernatural Het Fandom
There is het in the fandom, but the lack of recurring female characters as well as the focus of the story on the relationship between the brothers (no matter if you interpret it as brotherly or incestuous) keeps this part of the fandom relatively small. Favorite pairings include canon pairings Sam/Jessica, Sam/Ruby, Sam/Sarah, Dean/Cassie and of course, John/Mary, and fanon pairings such as Dean/Jess, John/Jo or Castiel/Anna. Crossovers with other fandoms mainly pair Dean with Faith or Buffy from Buffy the Vampire Slayer.
Mary Sue fic exists, although it is uncommon. However, Supernatural fandom does seem to produce significantly more original characters in its fanfiction than many other fandoms. This is likely a result of the narrative structure of the show itself, which provides a consistent stream of "guest" characters in canon. Much of the het fic in Supernatural fandom involves original characters (which are not necessarily synonymous with "Mary Sues," nor are they always female or love interests).
Another subset of het includes Winsister fic or AU stories involving one or more female Winchesters, often in place of either Sam or Dean. Sometimes these characters are female versions of Sam and/or Dean (Genderswap) while in other cases they are entirely original characters. Many, but not all, of these stories involving "het Wincest."
Communities
For more, see pages for specific pairings.
