Trap music in this connotation was characterized by soulful synths, 808s, the pan flute, sharp snares and long, syrup-slurred vowels. To take a step backwards, then, early '90s groups like Three 6 Mafia and UGK were making trap music before the term was coined. Many toss in Houston's DJ Screw and his "Chopped and Screwed" technique as well.
By the time Trap Muzik was released, trap seemed to have found its heart in Atlanta, and rappers Gucci Mane and Young Jeezy gained popularity in coming years. In 2005, Jeezy emerged with group Boyz n da Hood and further cemented his status as a "trap rapper" on his solo work Let's Get It: Thug Motivation 101. Gucci Mane exploded with "So Icy" from his '05 debut Trap House.
More recently, Gucci protégé Waka Flocka Flame and producer Lex Luger teamed up to define and further morph the genre. Luger's signature glittery ascending synth, beefy and aggressive bass lines and Flocka's bark collided to create a coked-up monster of a sound. Their highly addictive songs have dominated hip-hop in recent years and thus have been, naturally, appropriated.
In fact, in recent months electronic dance music producers began fostering their own version of trap. "It began blowing up heavy [in L.A.] in May or June," says L.A. Weekly columnist Jeff Weiss. On Weiss' blog, writer Son Raw praises Diplo-led label Mad Decent affiliates UZ and Baauer as heading up the new breed of producers making "trap out[side] the trap."