The definition of appositive refers to two nouns or noun phrases that are together in a sentence and each one gives more information about the other.(adjective)
In the sentence “I am waiting for my friend Beth” the phrase “my friend” is an appositive phrase to “Beth” and “Beth” is an appositive noun to “my friend”.
See appositive in Webster's New World College Dictionary
See appositive in American Heritage Dictionary 4
Learn more about appositive