If it's unplugged, it's acoustic. And Acoustic doesn't necessarily mean acoustic guitar. This genre of the blues is played on any non-electric instrument -- from guitar and banjo to harmonica and jug. It's played in any regional style -- Chicago, Delta, New Orleans, Texas -- and any musical style -- slide, ragtime and fingerpicking. Earlier-century maestros like Big Bill Broonzy, Lead Belly and Blind Lemon Jefferson are considered Acoustic, as are contemporary favorites Keb' Mo', Taj Mahal and John Lee Hooker.