A problem novel is a story that is written to show what it's like to experience a big issue or problem that many people face. It's like learning about a very important thing, but it's more fun because you get to read a story with characters and a plot.
These books are often written for kids around your age, to help them understand and cope with big problems like bullying, discrimination, or difficult family situations. The author wants to help you understand what's really going on in the world around you, and help you feel like you're not alone in dealing with these issues.
The most important thing to remember about problem novels is that even though they could be about tough topics, they're always written with hope and a way to learn from the characters' experiences. So you might feel some tough emotions while reading them, but in the end you'll usually feel better because the story has helped you learn how to deal with the problem.