Fan fiction is like telling stories about your favorite characters in a new adventure that you make up in your head. You can write about what they do after a movie or a book, or you can put them in a completely new and different world. It's like playing pretend with your toys or friends, but you write it down on paper or on the computer instead of acting it out. Just like with regular fiction books, you can create your own characters and your own storylines, but in fan fiction, you use characters and worlds that already exist in books, comics, movies, or TV shows that you love. It's like taking those stories and changing them a little bit to make them your own. People who really enjoy fan fiction like to share their stories with others who also love the same characters and worlds. Sometimes, people even write fan fiction about fan fiction! It's a fun way to explore your imagination and share your ideas with others who enjoy the same things.