Inscribed sphere

Imagine you have a big ball, like a basketball. Now, put a smaller ball inside the basketball so that the smaller ball is touching the inside of the basketball all the way around. This smaller ball is called an inscribed sphere.

The reason it's called "inscribed" is because it is inside the bigger ball, and all the points on the sphere are touching the inside of the bigger ball. It's like the smaller ball is written or drawn inside the bigger one.

Now, when someone talks about an "inscribed sphere" in math or geometry, they are usually talking about a shape that is not a ball, but has a similar idea of a sphere that is touching all the sides of the bigger shape inside of it.

The inscribed sphere is helpful in math because it can help us find things like the volume or surface area of the bigger shape. It's like the inscribed sphere is a clue to help us solve a problem!