The set of sheep,
the set of knots and the set of notches all have the same size;
they can be tallied by a one-to-one correspondence. The number name
five (5) is given to each of these sets. The cardinal number of
the set is said to be 5.
In common usage, a cardinal number is a
number used in counting (a counting number), such as 1, 2, 3, ....