What is the meaning of Undulation?

An instance or act of undulating.

A wavy appearance or outline; waviness.

A tremulous tone produced by a peculiar pressure of the finger on a string.

A wavelike curve; a smooth and regular rise and fall.

A wavelike motion of the air; electromagnetic radiation.

A feeling as if of an undulatory motion about the heart.

The distinctive motion of the matter within an abscess on being pressed when it is ripe for opening.

Source: wiktionary.org