Originally Posted By: dalehileman
Pook: No I believe it can also mean back-and-forth

http://dictionary.reference.com/search?q=undulate&r=66


Nevertheless, undulate always applies to a surface, never to the period of a pendulum or the results of social polling as 'swing' can. It means to ripple or roll or sway like a wheatfield in the breeze. Most often it is applied to the appearance of geography as you move through a series of rolling hills - 'undulating countryside'.