Slash fiction is a type of writing about characters from movies, TV shows, books, or video games whose romantic or sexual relationships have been changed so that they are together instead of separately. For example, if two characters in a TV show are not romantically involved, but the writer of the slash fiction story wants them to be, they would write a story where the characters are together romantically. It's a fun way to explore relationships between characters that may not be possible in the original story.