cardinality in set
The cardinality denotes the number of elements or cardinality of the set. (ie its size or length)
<MATH>\Large |S|</MATH>
The set has a cardinality of 4.
A finite set is a set that you can count.
If A and B are finite sets then <MATH> \Large |A \times B| = |A| \times |B| </MATH> where x denotes the cross product