A-a-a, what criteria are used to define them? How can they be distinguished? :D
Would such a definition suit you? :)
P.S. Just don't ask how to determine the quality of music, how original it is, etc.! :D
Bow down and hear our cry,
Our earthly rulers falter,
Our people drift and die,
The walls of gold entomb us,
The swords of scorn divide,
Take not thy thunder from us,
Take away our pride.
G.K. Chesterton: English Hymnal