A set, informally, is a collection of things. The "things" in the set are called the "elements", and are listed inside curly braces. For instance, if I were to list the elements of "the set of things on my kid's bed when I wrote this lesson", the set would look like this:
A set is a collection of things, usually numbers. We can list each element (or "member") of a set inside curly brackets like this:
set can be combined in a number of different ways to produce another set