Welcome JB. (oh by the way don't mind the current argument in the "not worth opening" thread. We do this every 5 weeks!)

Like folk music, you're going to find it difficult to get an actual definition of blues. You may however get lots of opinions. With any luck you WON'T get Broonzy's "horse" line. (don't ask. I'm sorry I mentioned it!)
For what it's worth, W.C. Handy claimed to have "invented" blues, and Brownie McGhee said "I AM the blues" (so did Willy Dixon) They've both left us now so we'll never know who was right! Thousands of singers have "got the blues", and an equal number were "born with the blues". (Perry Bradford titled his autobiography that way.)

Personally I like "country" blues (a term made up by white collectors in the sixties) and artists like Blind Boy Fuller, Willie MacTell, Son House, Robert Johnson, and Bill Broonzy. Hundreds more actually. There's always been an argument about whether white people can be blues singers. Me? Don't see why not.
Have fun at Mudcat.
Rick