origin: [early 1600's] Latin; ululatus; past participle of ululāre= to howl or shriek.
You may know this as the "Xena" war cry, but it's a sound that exists in many cultures. The simplest way to describe it is as an undulating (wave-like) shout; a shrill cry that is back & forth between different pitches -- not a musical type of baying like yodeling.
It's a sound found in nature as well, examples being: coyotes, wolves, and owls.
The word can be thought of exclusively as a mourning sound, expressing extreme grief (such as a funeral), although throughout Africa and the Middle East ululating is also a sound used in celebrations and ceremonies. In short, the sound punctuates an important event; it's a small, non-verbal announcement!
People in Africa demonstrate ululating.