Cardinal number
In mathematics, people also study infinite cardinal numbers. The first infinite cardinal number was named  (pronounced "Aleph null", "Aleph-zero" or "Aleph-naught") by Georg Cantor.  is the number of numbers that are in the group 0, 1, 2, 3, ... (which goes on forever). Both the set of natural numbers and the set of rational numbers are of size  (that is, they are both countable).