Wiktionary
n. (context music English) Any of the notes (flats and sharps) produced by the black keys on a piano or similar keyed instrument.
Wikipedia
Black Note were an American jazz ensemble formed in 1991. The band released four albums, on Columbia Records, Impulse! Records, Red Records and World Stage.
They won first prize at the John Coltrane Young Artist Competition in 1991.
Usage examples of "black note".
Tonks, who at once took out his black note-book, licked his thumb and flicked over the pages till he came to an empty one.
You would be responsible for the ruination of your closest friend, David Shawcross, and end his distinguished publishing career on a black note.
She had a black note-book in her hand, taken from a drawer in one of the Japanese cabinets, and was turning its pages mechanically.