An allegory is like when you tell a story that is kind of like a secret code. It's a way of saying something without saying it directly. In Renaissance literature, people liked to use allegory a lot.
Imagine you have a story about a tree. The tree seems like a regular tree but really it's supposed to mean something else. Maybe it stands for knowledge, or strength, or something like that.
So when you read a story with an allegory, you have to try to figure out what each thing in the story is supposed to represent. Sometimes it's easy to figure out, like in a fable where the animals are really supposed to be people. But sometimes it's really hard, and people argue about what everything is supposed to mean.
People liked using allegory in the Renaissance because it made their stories have deeper meanings, and it made people think more about what they were reading. It was like a game, trying to figure out what everything was supposed to represent.