The millennial whoop is a vocal melodic pattern alternating between the fifth and third notes in a major scale, typically starting on the fifth, in the rhythm of straight 8th-notes, and often using the "wa" and "oh" syllables. It was used extensively in 2010s pop music.
In the slavishly playlisted, gnat's-attention-span world of daytime radio, the Whoop has become a signalling device, often cropping up bang on cue around the one-minute mark, saying: "Hey wait! Don't run away just yet!"
The term was coined by the musician Patrick Metzger, who described it in a blog entry on The Patterning in August 2016. He suggested that, while the millennial whoop gained popularity from the late 2000s to 2010s, it has probably always been around. An earlier use can be heard in the 1983 song "Jungle Love" by The Time.
The 2017 song "Millennial Whoop" by American rock band the Pilgrims was written as a response to the idea of older generations looking down upon the younger for using such tropes: the song makes use of the interval pattern.