Consumption: one listener can stream a song a million times, but a million listeners can also stream a song once. The consumption here is the same - both total one million streams. An example metric would be streams.
Reach: the difference between one listener streaming one song a million times and a million listeners streaming a song once is in the number of people the song is reaching (i.e. 1 vs 1M listeners). An example metric would be monthly listeners.
Fandom: usually composed of an artist's most loyal audience, these are the fans who have been following an artist for the long term. An example metric would be followers.
Engagement: how closely an audience interacts with an artist, this encompasses an artist's current relevance and the direct activity they have with their fans. An example metric would be likes.