undulation

Short definition from Wiktionary

Noun

1. 1
   An instance or act of undulating.
2. 2
   A wavy appearance or outline; waviness.
3. 3
   A tremulous tone produced by a peculiar pressure of the finger on a string.
4. 4
   A wavelike curve; a smooth and regular rise and fall.
5. 5
   A wavelike motion of the air; electromagnetic radiation.
6. 6
   A feeling as if of an undulatory motion about the heart.
7. 7
   The distinctive motion of the matter within an abscess on being pressed when it is ripe for opening.