An appositive is a noun or noun phrase that renames or identifies another noun or noun phrase. It's often set off by commas, parentheses, or dashes.
Examples:
* My brother, John, is a doctor. (John is the appositive that identifies the brother)
* The city of London is a major financial center. (City of London is the appositive that identifies the city)
* The company's new product, a revolutionary smartphone, is already selling out. (revolutionary smartphone is the appositive that explains what the company's new product is)
Appositives provide additional information about a noun, making your writing more precise and clear.