Bag as A Data Structure
Bag is one of the fundamental data structures worthy of note, albeit less often mentioned like set, sequence, queue, stack, linked list, etc.
A bag is an unordered collection of items, which may contain duplicate items.
As its name nicely suggests, one can add items to it, and iterate over all items (hence an iterable). But it does not support remove API, like, a piggy bank.
A bag also allows duplicates, unlike its cousin set. Because of this, it is sometimes also called multiset.