Описание тега unordered-multiset
Use this tag for questions related to the unordered multiset, either it has to do with std::unordered_multiset of C++11, or with a custom implementation.
Currently all the questions with unordered-multiset are related to std::unordered_multiset, a container introduced in C++11. However, users attempting to build their own custom implementation of that container, are also welcome to use his tag.
Quoting cplusplus:
Unordered multisets are containers that store elements in no particular order, allowing fast retrieval of individual elements based on their value, much like unordered_set containers, but allowing different elements to have equivalent values.
cppreference.com also has a dedicated entry to this container.