Noun
(uncountable, fandom slang) Such fan fiction collectively.
(countable, fandom slang) A disclaimer or tag for a fan fiction, particularly on Archive of Our Own, meant to signify that the fan fiction contains the content that is described as being in it, and as such, readers shouldn't be surprised and shouldn't complain about finding said content therein.
(countable, fandom slang) A fan fiction that is particularly disturbing or disgusting due to its subject matter.
Source: en.wiktionary.org