An appositive adds additional information about a noun by restating or describing the noun and is usually set off by commas. Appositives can be used to combine multiple clauses or sentences into a single sentence to provide information in a concise way. Proper punctuation, including commas, dashes or parentheses, should be used to set off the appositive depending on its position in the sentence. Appositives are a useful grammatical tool to efficiently provide context or details about a noun.