An appositive phrase is a type of noun phrase that follows the noun or pronoun it modifies and amplifies or restricts its meaning.
Our department head, a careful reader and outspoken critic, will review the memo before it is circulated.[The italicized phrase is an appositive.]
Appositive phrases are similar to relative clauses; to avoid wordiness, relative clauses can often be reduced to appositive phrases.
As with adjective phrases, punctuation with appositive phrases is determined by whether the phrases are restrictive or nonrestrictive.