(noun) A condition that arises from repetitive slapping or striking of a lighter-skinned female gluteus maximus (butt, ass) while two individuals are engaged in a form of sexual intercourse commonly known as "doggy syle". In order to be considered a "Piano Booty", one cheek becomes bruised while the other remains white (or light colored) closely resembling the keys of a Piano keyboard's black and white sharp and standard keys respectively.
That girl is showin off her Piano Booty after last night.
by MGoBlue2009 August 28, 2009