Some examples of appositive nouns are "the girl, who has red hair" and "my brother, Jimmy." An appositive noun is a noun or noun phrase that immediately restates the noun adjacent to it. In the first example above, "the girl" is the noun, and "who has red hair" is the appositive noun phrase.
An appositive is always used with commas, and it must always be directly next to the noun or noun phrase it renames. An appositive gives information that is either essential or additional to the meaning and intention of the sentence, although it is not necessary to make the sentence grammatically correct.
There are two types of appositive nouns. The first is a restrictive appositive, which provides essential information to identify to adjacent noun it is modifying. An example would be "Carol's cousin, Hannah." Carol could have many cousins, but the appositive noun "Hannah" indicates which cousin is being referred to.
The second type of appositive noun is the non-restrictive appositive. It gives additional information that is not necessary to identify the original noun. For example, "My cat, who always hides my socks under the blanket, is sleeping in the sun." The appositive noun phrase, "who always hides my socks under the blanket," provides additional information about the cat but is not necessary for its identification.