What is an appositive noun?

An appositive noun is a noun or noun phrase that appears straight after another noun to specify what it refers to or provide more information.

If the appositive provides essential information (that is, it wouldn’t be clear whom or what you were talking about without it), then no punctuation is used to separate it from the surrounding words: “Your friend David is here to see you.”

If the appositive just provides extra information that isn’t essential to the meaning of the sentence, it’s set off with commas: “My hometown, Lochem, is quite small.”