These placeholders typically function grammatically as nouns and can be used for people (e.g. John Doe, Jane Doe), objects (e.g. widget), locations ("Main Street"), or places (e.g. Anytown, USA). They share a property with pronouns, because their referents must be supplied by context; but, unlike a pronoun, they may be used with no referent—the important part of the communication is not the thing nominally referred to by the placeholder, but the context in which the placeholder occurs.