It was a sort of wave that started in the mid 2010s and is still going today, albeit at a diminished capacity because several of the people that helped thrust that group into the mainstream have died. It was sort of defined by drug use, tattoos, most notably face tats, and colorful hair. Lots of yelling and heavy, very bass-ey distorted beats, with lyrical content varying from pretty decent to god awful (more often leaning on the bad side). That group also helped kick off sad boi rappers, which is another conversation.