Source: cirosantilli/cardinality
= Cardinality
The size of a set.
For <finite> sizes, the definition is simple, and the intuitive name "size" matches well.
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>.