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.

(of a sound) to rise and fall in pitch

the wail of a siren undulating in the distance.

to cause to move in waves.

to give a wavy form to.

Also, undulated. having a wavelike or rippled form, surface, edge, etc.; wavy.