cardinality

But if you can assign exactly one seat to each person, then both sets are exactly the same size and thus have the same cardinality.

It seems that the property of thought that the article describes might better be called “generalized quantity,” “comparative quantity” or “generalized cardinality.”

As Cantor was able to show, the cardinality of the natural numbers is the smallest possible infinity.

We don’t have to worry about mixing up the value of the number—its cardinality—with the order in which it arrives—its ordinality—since they are essentially the same thing.

Alternatively, it could be termed something else: cardinality, for example.