Definition
Cardinality
Cardinality is the number of elements in a set—its mathematical “how many”.
What it means
Cardinality is a set’s size. You can spread its objects out, bunch them together, or count them in a different order. If no element is added or removed, the cardinality stays the same.
Remember it
Move the set around; its “how many” stays.
Example
Seven buttons are first placed in a tight circle and then in a long row. Both arrangements contain the same seven buttons, so the set’s cardinality is 7.
Watch for
A row can look longer after the gaps grow, but spacing does not change cardinality.
Common mix-up
Cardinality answers “how many?”; an ordinal number answers “which position?”.
Exact meaning
The cardinality of a finite set is the number of distinct elements that the set contains.