Submultiset vs. Multiset — What's the Difference?

A subset of a multiset.

In mathematics, a multiset (or bag, or mset) is a modification of the concept of a set that, unlike a set, allows for multiple instances for each of its elements. The number of instances given for each element is called the multiplicity of that element in the multiset.

(set theory) A generalized type of set in which multiple occurrences of an element are permitted.