MathWorld may or not be what you are looking for, but it looks like a good reference site, for short takes on a large number of math topics. Good graphics too.

Caveat: only viewed it briefly until now.

Last I saw, it was part of Wolfram, though maybe independent earlier.

Check the About page for a good overview.

https://mathworld.wolfram.com/

https://mathworld.wolfram.com/about/