Answer: The bolded word ("clarinet") is used as an appositive.
Explanation: An appositive is a noun or a noun phrase that is included in a sentence in order to rename another noun or noun phrase that is found next to it. Appositives are generally nonrestrictive, that is to say they are separated from the rest of the sentence with commas; however, appositives can also be restrictive. The bolded word in the sentence provided ("clarinet") is used as an appositive because it is renaming the noun phrase "a woodwind instrument". Moreover, it is a nonrestrictive appositive because it has been separated from the other elements in the sentence by means of a comma.
