Here is the poster we made with realistic fiction explained by grade 4 and a definition from study.com
Grade 4: "Part of it (the story) is real and part of it is made up by the author. Characters and settings are imaginary. Some real facts may be in (the story). Write combines these two things (real and made up elements).
Study.com: "Realistic fiction is a genre consisting of stories that could have actually happened to people or animals in a believable setting. These stories resemble real life, and fictional characters within these stories act similarly to real people. They describe our world and our society."