Answer:

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, ....