We as writers make use of this term all the time when we write..
Whether you write music, poetry or just in general then you have made use of this term before.
You all of coarse know that in order to undulate a verse or a poem it has to rhyme so that the words will flow properly when said.
I for instance write music, hip hop preferably that I add my own style to, and when I’m writing Ill sometimes make a verse to wordy that when attempted doesn’t undulate right.
Every word has a place on the beat so if the words don’t correlate with the beat it won’t be able flow.
Undulate, to flow or move in a wave like motion.