Set

A set is a collection of related things. It doesn't have to be just numbers!
When a set is listed, it's members are usually listed between curly brackets, like these: { }
Here are a few sets:

1. Members of a class whose names start with L: {Lacie, Luke, Lauren}
2. Days of the week: {Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday}
3. Colors of the rainbow: {red, orange, yellow, green, blue, indigo, violet}
4. Whole numbers between 3 and 10: {4, 5, 6, 7, 8, 9}
5. Daily high temperatures in the first week of February: {53, 48, 49, 55, 44, 51, 54}

They can be things or numbers. They can be a collection of almost anything you can think of.

It's a pretty loose concept!