Yes, an appositive is a noun (or noun phrase) that renames or describes another noun. It's used to provide additional information about the noun it's next to.
The commas are important:
* Essential Appositives: If the appositive is essential to understanding the noun, it's not set off with commas. For example: "My friend John is coming over." Here, "John" is essential to identify which friend is coming over.
* Non-Essential Appositives: If the appositive provides extra, but not crucial, information, it is set off with commas. For example: "My friend, John, is coming over." Here, we already know which friend is coming; "John" just adds extra information.
In short, an appositive is a noun that renames or describes another noun. Whether it's set off with commas depends on whether it's essential to the meaning of the sentence.