An ornament that consists of rapid alternation between one tone and another tone either a step or a semitone away from the first tone.A rapid alternation between the specified note and the next higher note (according to key signature) within its duration. Also called a "shake." When followed by a wavy horizontal line, this symbol indicates an extended, or running, trill. In much music, the trill begins on the upper auxiliary ornament consisting of a rapid alternation between two pitches, the main pitch, and the pitch a whole or half step above it