Technically refers to fan fiction, stories written by fans on existing works. However, in the impro community, the term has broadened in meaning to include stories that aren't based on particular works.
a story that is written by a fan and is based off of an established continuity, solely for the purpose of continuing the story or altering the storyline
Short for "fan fiction," this is a fictional story written by a fan about a particular show. While many focus on relationships between characters, others focus on furthering certain plotlines of the show.