Simplicial set

Okay, so imagine you have a bunch of Lego blocks. Each block has different colored squares on it, and you can build things by sticking the blocks together.

A simplicial set is kind of like that. Instead of Lego blocks, we have a bunch of mathematical objects called simplices. Each simplex has a certain number of vertices, which are like the corners of the block.

We can stick these simplices together to make bigger shapes, just like we stick Lego blocks together to make bigger structures. And just like with Lego blocks, we can think about how the vertices of each simplex are connected to each other.

So a simplicial set is basically a collection of these simplices, all stuck together in different ways. We can use these sets to study all sorts of different things in math, like topology and algebra.

But don't worry if you don't understand all that yet – it's a pretty tricky concept, even for grown-ups!