Closed regular set

So imagine you have a bunch of toys on the floor, but you want them to be in a neat box so they don't get lost or messy. That box is like a closed regular set.

Now let's say you only want certain toys in that box that are your favorite, like your teddy bear or your doll. Those toys are the points in the closed regular set, and the box is closed because it contains all the points inside it.

Basically, a closed regular set is like a container that holds all the points you want inside it, and nothing else is allowed to come in or out of that container. It's like making sure your toys stay in order and don't get lost.