Mumble

Mumble rap is a loosely defined style and era of hip-hop that emerged and proliferated via the online audio distribution platform SoundCloud during the mid-to-late 2010s. The term originated as a pejorative used to describe a vocal style characterized by unclear or incoherent enunciation, often described as "mumbling", which represented a shift away from traditional hip-hop conventions centered around complex or meaningful lyricism, and instead emphasizing other aspects of delivery like melody, mood, and tone.

Excerpt from Wikipedia: Mumble rap. Content available under CC-BY-SA 4.0.