Defining musical genres

Define “rock” vs “pop”for me. (Thanks in advance for your input)
Is Madonna a “pop” or “rock” artist? How do you all distinguish between those terms? Is it an important distinction in any way?
In the folkie community the definition of “folk” music has been a subject of much debate – I always went with “I know it when I hear it”.

Check out allmusic.com

Rock music generally requires a certain set of instruments–a guitar or two, a drumkit, and maybe a bass. By that standard, a lot of Madonna’s work doesn’t qualify. But there is a significant overlap between rock and pop. allmusic’s breakdown by genre is generally good at a high level, so you might take a look there.

This is the only accurate definition (a variation of Damon Knight’s “Science fiction is what I’m pointing to when I say ‘this is science fiction’”).

It is next to impossible to create a definition of a genre that will include everything you consider part of that genre and eliminate everything you don’t think is part of that genre. So you end up pointing.