Realistic Fiction can be described as A book or story that is written as though it is nonfiction, for example, The Fault in Our Stars. When reading the story, there is no fantasy, or aspect of it that come off as hard to believe. But nonetheless, it fiction. Hence why is it called Realistic Fiction.
Realism as described by https://www.shmoop.com/realism/, is Realism is a literary movement that developed in the middle of the 19th century in France and then spread like wildfire throughout the rest of Europe, all the way to Russia, and then overseas to the US.
Realism, as you might guess by its title, is all about portraying real life. Realist writers write about regular folks—bored housewives, petty government officials, poor spinsters, poor teenagers—living ordinary lives. Let's face it: most of us don't live crazy exciting lives, after all. What Realist writers are really good at doing is showing us how even ordinary lives are meaningful, and—hello—always full of drama.