Realism in theatre means that the play or performance tries to be like real life. It's like when you play house with your friends and you pretend to cook food and clean up and talk to each other like real grownups would. In a realistic play, the actors try to act like real people and talk and move in a way that you might see in real life. They might use props and costumes that look like the ones real people would use, and the set might look like a real room or place. The goal is to make the audience feel like they're watching a real-life situation instead of just watching something fake.