the act of undulating; a waving motion or vibration; as, the undulations of a fluid, of water, or of air; the undulations of sound.-a wavy appearance or outline; waviness.-the tremulous tone produced by a peculiar pressure of the finger on a string, as of a violin.-the pulsation caused by the vibrating together of two tones not quite in unison; -- called also beat.-a motion to and fro, up and down, or from side to side, in any fluid or elastic medium, propagated continuously among its particles, but with no translation of the particles themselves in the direction of the propagation of the wave; a wave motion; a vibration.