As Billboard wraps up Chorus Week, we're looking at the classic, stupid-catchy and often mind-blowing melodies that have defined the Korean pop world in the 21st century. K-pop listeners know that the right hook can create a viral sensation (just ask PSY), and the following 10 choruses not only got stuck in listeners' minds and hearts, but did so by bringing refrains that were progressive and undeniable to the scene.

Read on to see the full list of the top 10 K-pop choruses of the 21st century (referring to 2000 and beyond) and skip right to the chorus of each entry in the embedded YouTube link.

10. EXO, "Growl"

The sensational EXO has provided some of K-pop's greatest modern-day choruses (2015's "Call Me Baby" and last year's "Monster" were all contenders for this list), but it's nearly impossible to deny their breakout hit "Growl." The refrain opens with a boy-band sound that brings to mind a modern-day *NSYNC, but becomes EXO's own by the end with its eccentric "I growl, growl, growl" hook that illustrates why it's always worthwhile to experiment in K-pop.

9. Brown Eyes, "Already One Year"

A standout track from the male duo's self-titled debut album, the band crafted a chorus that curled into listeners' hearts. They crooned in English and Korean, "I believe in you / I believe in your mind... / Even after a year or a year after that / I will wait for you," setting a new standard for ultimate devotion for Korean ballads.

8. Orange Caramel, "Catallena"

A representative song of how twistedly brilliant K-pop choruses can be, the quirky female trio sing about being captivated by the mysterious "Catallena" woman over a mix of Bollywood-inspired disco beats, funk guitar and a sample of a traditional Punjabi wedding folk song "Jutti Meri Jandiye." The girls' melodious, baby-coo deliveries and queer-leaning lyrics are almost an afterthought when you consider this jarring-yet-genius chorus.

7. Wonder Girls, "Tell Me"

One of the first K-pop songs to define what it meant to go viral, "Tell Me" was one of Wonder Girls' early breakout hits with a chorus that anyone could sing. The repetitive "tell me, tell me" lines were the gateway drugs to letting oneself belt along to the more vocally challenging sections, making this a K-pop karaoke classic.

6. Super Junior, "Sorry Sorry"

Super Junior's super-successful hit parlayed into one of K-pop's most recognizable dance moves (the shuffling of one's hands on the chorus, as seen by the members in the music video). Despite being extremely repetitive, "Sorry Sorry" still kept a sense of slickness and sophistication. With its release in 2009, it's now become a bit of a badge of honor among international K-pop fans who can judge how deep someone's ingrained in the scene if they can recognize the "Sorry Sorry" dance. Like "Growl," this came from Korea's biggest pop supplier, SM Entertainment.

5. Big Mama, "Betrayal"

While Big Mama may have initially stood out for being bigger than most Korean singers, what has kept their legacy alive is their stunning vocals that parlay into heart-wrenching choruses. Their 2007 single "Betrayal" is an emotional confessional from a woman who's done her lover wrong, marking a chorus that as difficult to swallow as it to correctly sing. Nevertheless, it's a stunning standout in the K-pop world.

4. Park Jiyoon, "Adult Ceremony"

In today's K-pop scene, "Adult Ceremony" is a song that stars perform to prove they can pull off mature performances (see Twice or BTS). But when this track dropped at the turn of the 21st century, it was one a defining anthem with Park Jiyoon declaring she wasn't a little girl anymore. The track boasted a truly chewy bubblegum chorus, but the syncopated vocal rhythm gives it additional sense of mystery making it all the more superbly sexy. Years later, Brown Eyed Girls would also create another equally unforgettable sexual empowerment anthem with 2009's "Abracadabra," but you can't deny "Adult Ceremony."

3. BIGBANG, "Lies"

While the phenoms have created some of K-pop's most recognizable hits, when it comes to strictly choruses, BIGBANG's "Lies" is the true standout. The blend of boy-band harmonies and hip-hop chants marked something fresh for the scene in 2007, and situated the song's writer and producer G-Dragon as a true mainstream force.

2. DJ Doc, "Run to You"

One of the earliest indicators of the potential of K-pop's universal appeal, DJ Doc's megahit from 2000 blended a high-energy hip-hop sound with a simple, melodic refrain that got into all of South Korea's head. The success of this track, and its undeniable chorus, was all the more remarkable given rap had yet to be truly accepted in the Korean mainstream. The trio not only solidified the burgeoning potential of hip-hop in K-pop, but also signified the importance of genre-blending for mass appeal, which would be a cornerstone in Korean music's international expansion.

1. Girls' Generation, "Gee"

Arguably every section of Girls' Generation's sensational 2009 single could be an excellent chorus, making its official one all the more impressive and important to explore. Before it hits, the listener has been submerged in GG's world of "Gee" (see what they're doing here?) with the repetitive "gee gee gee gee, baby baby" hook peppered through the verses, all leading up to a saccharine explosion that kicks off the chorus. A powerful blast of synthesizers welcomes us into the refrain, seemingly signaling how big this section will, guiding us through though the ladies singing and chanting lines about being unexpectedly in love.

Before "Gangnam Style" mania, "Gee" was the top-viewed K-pop video on YouTube and a major part of that addiction was its centerpiece of a chorus that captured the heart of a new generation of fans that were either enamored with the adorable ninesome or wholly intrigued by something that felt both refreshing and a wink to pop's simpler, bubblegum past.