An appositive (also called an appositive noun or appositive phrase) is a noun phrase that follows another noun phrase and provides additional information about it. The two words or phrases are described as being in apposition.

The usual structure is the antecedent (a noun phrase that the appositive will give more information about) followed by the appositive itself, either set off by commas or, if it’s essential to the meaning of the sentence, without any additional punctuation.