defining GOOD!

So how do you actually define what's good?!! I have been trying to figure this out for a while by now. When people ask me what music do I listen to, I instantaneously say, " GOOD music!" And when they ask me what books do I read, "GOOD books," is my top of the mind answer. The definition of "good" keeps changing for me as per my mood and state of mind. And, everything is relative!