The verb undulate comes from the Latin word undula, which means "wavelet" (unda means "wave"). So any action shown with the verb undulate has that waving sense to it. If something moves in a wavy, pattern, for example, it is said to undulate.

What causes undulation?

It is caused by a bacterium called Brucella that can be transmitted in unpasteurized milk or cheese of cattle, sheep, and goats or by contact with diseased animals.

What is undulate motion?

verb (used without object), un·du·lat·ed, un·du·lat·ing. to move with a sinuous or wavelike motion; display a smooth rising-and-falling or side-to-side alternation of movement: The flag undulates in the breeze. to have a wavy form or surface; bend with successive curves in alternate directions.