Fanfiction writers take fictional characters and settings from fictional (or sometimes historical) stories that were created by other people, and write original stories about them. People write fan fiction for a many different book, television series or movie fandoms.
When fanfiction first began, it was often only published in fan magazines. Today fanfiction, like many fandom activities, can be usually found on the internet. This has created many fanfiction communities. People in these communities post their fanfiction and receive feedback (reviews) from other community members.
There is also fan art (also called fanart), which is often drawings or other visual art based on a fandom.
Fan fiction Facts for Kids. Kiddle Encyclopedia.