A theme is the main idea or message that a story or piece of writing is trying to convey. [idea: a thought or concept]
For example, in the book “To Kill a Mockingbird,” the theme is about the importance of empathy and understanding towards others, even if they are different from you. [empathy: the ability to understand and share the feelings of another]
Very Simple Definition:
A theme is the big idea of a story. It’s what the story is all about.
For example, in the story of “The Three Little Pigs,” the theme is about the importance of hard work and planning ahead.