As David Bromberg said: "You've got to suffer if you wanna sing the blues". I'm no expert on the blues, but I think it's expanded from the "suffering" aspect; not entirely "cry in your beer music", (which is my definition of commercial country/western, but that's another thread). What about "talking blues"? Some of those are hilarious, e.g. "Talking Candy Bar Blues", "Dying Cub Fan's Last Request" and the "Vietnam Potluck Blues". The crossovers to jazz and rock are plentiful, hmmmm... I think you just know it when you hear it. I don't think I can exactly define it, but as I said, I'm no expert. Click here for a perfect definition. (;