Voiced labial–velar approximant
A voiced labial–velar approximant is a type of consonantal sound, used in some spoken languages. It is the sound denoted by the letter ⟨w⟩ in the English alphabet; likewise, the symbol in the International Phonetic Alphabet that represents this sound is ⟨w⟩, or rarely [ɰʷ].
Source: Wikipedia — Voiced labial–velar approximant (CC BY-SA 4.0)