I'm wondering what "Rock" genre of music refers to. 50's up until Alternative ? Yet we see Nirvana still categorized at times as "rock". It's a pretty ambiguous term now-adays, yet just how ambiguous ? I have no idea.  I always assumed Popular music was the broader category. It included all styles, oldies, and contemp music alike. In fact only styles I didn't ever think of as "popular" would've been certain styles of Jazz, and classical.  Than Boston "pops" came along, and I had to question that as well. It appears from compiled lists of "Top 500 rock songs", and this type of discussion, that I have NO concept of what "Rock" means any longer.  Is it a style of music ?   or a time period ?   Both ?
Than there's the category of "Metal",  I won't even begin to try to figure out how many dramatic adjectives synonymous with the term "death" have been used to give this genre a placing in the "different" realm.
 

  (I feel like Andy Rooney)