I know it's short for "independent", meaning not signed to a recording label, unless it's a small "Indy" label. 

I have asked 47 different people what "Indy" music sounded like, and got 47 completely different answers. They almost all boiled down to describing the band or artists' business model. I couldn't find two people who had the same answer to describing the sound of "Indy" music. 

I have a friend who has released about a half dozen CDs independently. He is a singer/songwriter. His music reflects influences that range from Jackson Browne, Dan Fogelberg, Harry Chapin, and even a zydeco version of the Beatles' You Can't Do That. So, does that mean "Indy" music sounds like that? I've encountered country bands and singers who aren't signed, who are "independent". Does that mean country is "Indy"? 

Several decades ago, Lisa Loeb had a hit video on MTV back when they played videos with Stay. It was a cute little girl-pop song, and since she was unsigned, that meant she was "Indy", so is girl-pop "Indy" music? 

If an independent band becomes successful and signs a major label and/or distribution deal, and ceases being "independent", is all of their music no longer "Indy", or just the new stuff they make after they've sold their souls to the man? 

It occurs to me that since I do some solo troubadour gigs, and I'm not signed, does that mean I'm "Indy"?