a tremble
A variation in the volume of a note or a chord, evoking a tremor or quiver.
The device in an organ that produces a tremolo effect.
A rapid repetition of the same note, or an alternation between two or more notes. It can also be intended to mean a rapid and repetitive variation in pitch for the duration of a note. It is notated by a strong diagonal bar across the note stem, or a detached bar for a set of notes (or stemless notes).