Betti number

A betti number is like counting how many holes a shape has. Imagine you have a block of Swiss cheese. If you look at it from the top, you can see lots of little holes. Each little hole is like a circle. If you count all the circles in the cheese, that's the betti number.

But you can also have bigger holes, like a tunnel through a mountain. That's like a bigger circle, and it counts for more betti numbers. So the more holes a shape has, the higher the betti number.

Scientists and mathematicians use betti numbers to study shapes and surfaces in many different fields, like biology, computer graphics, and engineering. It helps them understand the structure of the shape and how it works in the world around us.