The term 'SOURCE OF SOME RINGS' can be solved by two crossword solutions: 'ONION' (5 letters) and 'OIO' (3 letters). Onions are a type of vegetable that have a distinctive flavor and are used in many dishes. They are also a source of some rings, as they are often cut into thin slices to be used as a garnish or topping. OIO is an acronym for 'One In, One Out, ' which is a rule of thumb for managing inventory. This rule states that when a new item is added to inventory, an old item must be removed. This concept can also be applied to rings, as it ensures that the number of rings in a collection remains constant.