Yodeling is hard to describe, but everyone knows it when they hear it. When a singer holds a long note while wavering between their regular voice and their high falsetto voice, they’re yodeling.
Cowboy music is one genre that has used yodeling to great effect, as have Swiss, Austrian, and German folk singers. Other performers have billed themselves simply as yodelers — there have even been competitions for the best or longest bouts of yodeling. If you're not sure what yodeling sounds like, listen to the chorus of the song "The Lion Sleeps Tonight," or the famous Tarzan yell. Both are great examples of yodeling.