undulation

1. A regular rising and falling or movement to alternating sides; movement in waves.
2. A wavelike form, outline, or appearance.
3. One of a series of waves or wavelike segments.

A wavelike motion in any medium; a vibration.

The noun has 3 meanings:

Meaning #1: an undulating curve
  Synonym: wave

Meaning #2: wave-like motion; a gentle rising and falling in the manner of waves

Meaning #3: (physics) a progressive disturbance propagated without displacement of the medium itself
  Synonym: wave