Source : Webster's Revised Unabridged Dictionary (1913)

Undulation \Un`du*la"tion\, n. [Cf. F. ondulation.]
   1. The act of undulating; a waving motion or vibration; as,
      the undulations of a fluid, of water, or of air; the
      undulations of sound.

   2. A wavy appearance or outline; waviness. --Evelyn.

   3. (Mus.)
      (a) The tremulous tone produced by a peculiar pressure of
          the finger on a string, as of a violin.
      (b) The pulsation caused by the vibrating together of two
          tones not quite in unison; -- called also {beat}.

   4. (Physics) 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 : WordNet®

undulation
     n 1: an undulating curve [syn: {wave}]
     2: wave-like motion; a gentle rising and falling in the manner
        of waves
     3: (physics) a movement up and down or back and forth [syn: {wave}]