Appositive phrases describe nouns or pronouns. Instead of modifying nouns or pronouns, however, appositive phrases rename them. In form they are nouns or noun equivalents.
Bloggers, conversationalists at heart, are the online equivalent of radio talk show hosts.
Appositives are said to be “in apposition to” the nouns or pronouns they rename. Conversationalists at heart is in apposition to the noun Bloggers.