ELI5: Explain Like I'm 5

Compact group

Okay kiddo, let's imagine you are playing with a bunch of toys. You have a big toy box to keep them in, but sometimes you want to take some toys out and play with them. You can't take all the toys out at once, because there isn't enough space for them to move around and have fun. So, you have to pick a few toys that will fit in your arms and take them out to play with. This is sort of like what a compact group does.

In math, a compact group is a special kind of group that is like a big toy box for numbers or other mathematical objects. Just like your toy box, a compact group has limited space, so you can't fit an infinite amount of things inside it. But you can take out some things from the group and still have enough space for them to move around and play with each other. This means that the group is "compact" in the sense that it has enough space for the things inside it to interact with each other, but not too much space that they can just "float away" and be separate from each other.

Compact groups are really useful in math because they help us understand how numbers or other objects relate to each other. Just like a group of toys can help you understand how different toys can work together or influence each other, a compact group can help mathematicians understand how different numbers or other objects can work together or influence each other. So, even though a compact group might seem like a simple concept, it can actually help us solve some really complicated math problems!