What is "tremolant"

Tremolo \Tre"mo*lo\, n. [It. Cf. Tremulous.] (Mus.)

1. The rapid reiteration of tones without any apparent cessation, so as to produce a tremulous effect.

2. A certain contrivance in an organ, which causes the notes to sound with rapid pulses or beats, producing a tremulous effect; -- called also tremolant, and tremulant.