What is the definition of the term audience of one?

The term "audience of one" is, first, not a term. "Audience of one" is a phrase. The phrase was made popular for having been used in a song, and, later, as an album title. Rage Against the Machine, a rock band, recorded the song, "Audience of One". They wrote the song as a criticism of current Pop Music. Sadly, there is no one definition of the phrase.