The black keys on a piano are called “accidentals” or “sharps and flats”. They are called this because they can alter the pitch of a note and are not part of the natural major or minor scale. These accidentals derive their names from the fact that they raise (sharp) or lower (flat) the pitch of a note by a half-step. The naming of the black keys on a piano follows a specific pattern based on musical theory, which assigns each key a unique name based on its position in the musical scale.