Okay kiddo, let me tell you about Deligne-Mumford stack.
Do you know about shapes? Imagine you have different shapes like squares, circles, and triangles. Now imagine that these shapes can have layers on them or inside them, like a sandwich.
When we talk about shapes with these extra layers, we call them "stacks."
Similarly, Deligne-Mumford stack is a really fancy kind of shape, or "stack," that is used in mathematics to study things called "moduli spaces." Moduli spaces are like a way of keeping track of and understanding all the different types of a certain object.
For example, say you have a bunch of different types of cats--long-haired cats, short-haired cats, black cats, white cats. A moduli space would be a way of organizing and understanding all those types of cats.
The Deligne-Mumford stack does this for things called "curves." Curves are just fancy shapes that mathematicians like to study, and the Deligne-Mumford stack helps them understand all the different types of those curves.
It's pretty complicated stuff, but just remember--Deligne-Mumford stack is like a really fancy shape that helps mathematicians study and understand other shapes called "curves."