Definition from Wiktionary, the free dictionary
cardinality (plural cardinalities)
- (set theory) Of a set, the number of elements it contains.
- The empty set has a cardinality of zero.
- (data modeling) The property of a relationship between a database table and another one, specifying whether it is one-to-one, one-to-many, many-to-one, or many-to-many.
- (in set theory): power
Related terms 
in set theory