Simply connected

When we talk about something being simply connected, we are talking about its shape and how we can move around inside of it. Imagine a piece of paper that has no holes in it. We can draw a line on it and move around without ever having to lift our pencil or cross over the line we drew. This is called a simply connected shape.

Now imagine a donut. If we draw a line on the surface of the donut and try to move around it without lifting our pencil, we will eventually have to cross over that same line because there is a hole in the middle of the donut. This is not a simply connected shape.

So, when we say something is simply connected, it means we can move around inside it without ever having to cross over the same path we took before, just like on a piece of paper with no holes. It's like a maze where there is only one way in and one way out, and we never have to retrace our steps.