- any of the numbers that express amount, as one, two, three, etc. (distinguished from ordinal number).
- a number or symbol analogous to the number of elements in a finite set, being identical for two sets that can be placed into one-to-one correspondence: The cardinal number of the set a1, a2, … an is n.
- a number denoting quantity but not order in a set
- maths logic
- a measure of the size of a set that does not take account of the order of its members
- a particular number having this function
