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.
For more terms and definitions, check out the full music data glossary with over 80 terms here: https://learn.chartmetric.com/music-data-glossary