If my song is approved, does that mean that it will be on a compilation?

If your song is approved, that means that the song is available to be compiled on compilation albums.

From that point on, your song is available to all connected music curators to preview and to use on compilation albums. Approval doesn't mean that your song has already been compiled.

Nevertheless, you have the option to buy guaranteed placements on compilation albums, once your song has been approved.