I find always easier to explain the difference between Midi and Audio with the analogy of the Player piano.
Midi is what is on The Old Paper Rolls (What makes the piano play Music), with those holes are the "Midi Data" or note information, you may see it(Paper Roll), but do not hear it until the piano player is activated.
The Audio es when you Hear the Music from that Player piano, or when listening to a CD-MP3.