Good question Dave. And rock has had many iterations. For me, a kid growing up in the 70s, I guess I have a personal definition. But like you, I have wondered: what exactly is "rock"?
So here, as best as I can describe is my personal definition:
Its a vibe, that to me, was embodied when John Lennon yelled out "1234..."
A driven hard hitting sound, simple yet effective.
This year the diet is definitely gonna stick!