This was a messy year for pop music. Rules changed, hits were eccentric, and the whole twelve-month period felt enigmatic in a way we don’t usually expect from something as conventional as pop.

Pop stars—save for a guy named Aubrey and a girl named Ariana—were no longer the de-facto agenda-setters for a mass audience. And with the very definition of “pop star” and “mass audience” in flux, most music this year seemed to exist only in silos, playing loudly to a small subset of the population and lacking the universal quality we expect from pop trends. Yes, the whole world leapt perilously from their cars for the “In My Feelings” challenge—but that was the exception, not the rule. Overall, 2018 lacked big, unifying pop moments and an easily definable musical identity.

But this year also felt like the wobbly beginnings of something exciting and fresh. After Billboard finalized changes to its chart metrics in May, new artists and big hits could arise from anywhere—YouTube, Spotify playlists—and go directly to the top of the charts without ever needing a radio spin. Marquee acts like J. Cole let fans choose their singles, dropping surprise albums with no advance tracks, then servicing the most-streamed tracks to radio. Meanwhile, former unknown rapper Sheck Wes’s “Mo Bamba”—inconspicuously uploaded to Spotify over 18 months ago—meandered its way to the year’s most surprising top 10 track on the sheer power of word of mouth and streams.

And while a hit’s influence may have been more targeted than in years past, this longer tail of popular-music culture afforded some atypical starlets to emerge (take Tekashi 6ix9ine), strange songs to reach prominence (Travis Scott’s amorphous smash “Sicko Mode”), and a broader array of artists to find their specific niche (pop oddball Charli XCX and country hippie Kacey Musgraves, among others).

Indeed, the pop rule book was an open document this year. Here are some of the emerging new rules for pop during a highly transitional 2018:

From left, by Erika Goldring/WireImage, by Rich Fury/Getty Images, by Christopher Polk/Getty Images.

Hip-Hop Is Pop Music

For decades, hip-hop has played an outsize role in influencing American popular music—but it may have never been more evident, at least on the pop charts, than in 2018. Of the 49 weeks clocked by Billboard so far this year, 43 featured either a rap song or a song with a rap at No. 1, continuing a trend line of the genre’s increased centrality in mainstream pop. (In 2017, it was 33 weeks; in 2016, 31.) And, largely unprecedented, the six biggest debut album-sales weeks of 2018 all came from rappers: Drake, Travis Scott, Lil Wayne, Post Malone, Eminem, and J. Cole.

Much of this was driven both by ongoing changes in consumption habits, as well as some continued cultural shifts. Billboard’s altered metrics gave more weight to streaming, a space where a younger generation who grew up on hip-hop have the most influence, and where it’s by far the most popular genre.

Some fantastically bizarre success stories emerged as a result: Wes’s aforementioned brash “Mo Bamba”, XXXTentacion’s emo lament “Sad!,” and Kodak Black’s zany “Zeze,” all previously implausible crossover pop smashes, broke into the top 10. Cardi B’s song of summer, “I Like It,” was rapped primarily in Spanish, while Childish Gambino’s “This Is America” rose to No. 1 largely on the strength of its eloquent video addressing police shootings of unarmed black men. And one of the year’s most intriguing hits, Scott’s “Sicko Mode (feat. Drake),” was completely non-traditional in structure, split into three distinct movements, smash-cutting into one another with no central hook to speak of.