Noun
The act of undulating; a waving motion or vibration; as, the undulations of a fluid, of water, or of air; the undulations of sound.
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.
Source: Webster's dictionaryWind is a floating wave of air, whose undulation continually varies. Vitruvius
Her hair is troublesome and curly ... It falls in long, black strands, but each strand has a gentle, complicated undulation travelling through it, like a mild electric shock or a thrill, hat gives it a life of its own; it is visually analogous to a tremolo on a musical note. Amit Chaudhuri
A player can send the jack anywhere on the green in this game and the green itself is more akin to a golf green, with lots of undulation. Source: Internet
North of the Congo basin, and separated from it by a broad undulation of the surface, is the basin of Lake Chad – a flat-shored, shallow lake filled principally by the Chari coming from the southeast. Source: Internet
The course for the next four or five hundred feet had but little undulation. Source: Internet