Set theory

Set theory is a kind of math that's all about sets. A set is a group of things, like a group of friends or a group of animals. In set theory, you can combine different groups of things together and do math with them. For example, if you had two sets of things, A and B, you could figure out the things that are in both sets, the things that are only in A, the things that are only in B, and the things that are in either A or B but not both. That way, you can get a better understanding of how the sets are related to each other.