But for infinity, things are messier, e.g. the size of the real numbers is strictly larger than the size of the integers as shown by Cantor's diagonal argument, which is kind of what justifies a fancier word "cardinality" to distinguish it from the more normal word "size".
The key idea is to compare set sizes with bijections.
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Cardinality is a mathematical concept that refers to the number of elements in a set or the size of a set. It is used to describe the quantity of items in both finite and infinite sets. 1. **Finite Sets**: For finite sets, cardinality is simply the count of distinct elements.