What is the origin of the idiom "be an item" and when to use it?

The origin of the idiom "be an item" is not definitively known, but it likely emerged in the early 20th century. The term "item" here refers to two people being considered as a single unit or entity. "be an item" is used to describe two individuals who are romantically involved or in a relationship. It implies that they are recognized and acknowledged as a couple. It is commonly used in informal conversations or when discussing relationships.