title: What is a data structure which is unordered and allows repetitions called?
body: <p>Is there any "formal name" for data a structure with the following features:</p>
  
  <ul>
  <li>set/group which allows repetitions</li>
  <li>unordered (order has no significance)</li>
  </ul>
  
  <p>For example, a list is an ordered set/group with repetitions.</p>
  
  <p>In the set <code>{2,2,2,2,3,3,3,3,4,4,4,7,6,5,6}</code> there is no significance to the order so the an efficient way to implement is set with 2-d arrays <code>{[2,4],[3,4],[4,3],[7,1],[6,2],[5,1]}</code>.</p>
  
  <p>I am asking if there is any formal name to it ?</p>