The cardinality of a set A, written as |A| or #(A), is the number of elements in A. Cardinality may be interpreted as "set size" or "the number of elements in a set". For example, given the set we can count the number of elements it contains, a total of six. Thus, the cardinality of the set A is 6, or . Since sets can be infinite, the cardinality of a set can be an infinity. Being able to determine the size of a set is of great importance in understanding principles from discrete mathematics and finite mathematics, but other subjects as well, including advanced set theory and combinatorics.