What is cardinality?

Cardinality is just a fancy way of saying how many things are in a group.

Imagine you have a basket full of apples. If you count them one by one, 1, 2, 3… until you finish, you're finding the cardinality of that group of apples.

Think about your toy box. When you put all your toys out to play, you might line them up and say: “I have 5 cars, 3 dolls, and 2 blocks.” Each of those numbers, 5, 3, and 2, is the cardinality of each group.

Now imagine you invite a friend over. Both of you take out your toys and count yours separately. If both of you have the same number of toys, like 6 each, then your toy groups have the same cardinality.

But if one of you has more toys, say 7, then that group has a greater cardinality than the other.

It’s just counting, like when you count how many cookies are on the plate before you eat them!