From middle school classrooms to the walls of the Vatican, there's no escaping the "six-seven" phenomenon. Even for the pope himself.Pope Leo XIV participated in the viral "6-7" trend at the urging of a group of youngsters inside the Vatican on May 16."6-7" (also "six-seven" and "67"), is a slang phrase popularly used by Gen Alpha.While some interpret the phrase to mean "so-so" or "maybe this, maybe that," it is also used as an exclamation, according to a news release from Dictionary.com, which selected the term as its World of the Year in 2025.Watch video of Pope Leo doing '6-7' trendSee Pope Leo learn how to do the '6-7' memePope Leo joined a viral moment after kids showed him how to do the "6-7" meme during a visit in Vatican City.While greeting people gathered inside the Vatican on May 16, Leo met a group of children who declared, "Six seven." They also did the accompanying hand movement – holding both hands palm up and moving them up and down, like weighing two objects – that has become synonymous with the phrase.After a moment of hesitation, Leo repeated after the children, even doing the hand gesture. The children celebrated with applause as the pontiff continued to the next patrons.A video from the encounter, which was posted to TikTok by user Don Roberto Fiscer, has been viewed more than 23 million times as of May 18.What does '6-7' mean?"Six-seven" is a slang term used by school-aged children around the world.The phrase has become more of a viral refrain that a word with meaning, though some interpret it to mean "so-so" or "maybe this, maybe that," according to a news release from Dictionary.com."It’s part inside joke, part social signal and part performance," Steve Johnson, director of lexicography for the Dictionary Media Group at IXL Learning said in a news release. "When people say it, they’re not just repeating a meme; they’re shouting a feeling. It’s one of the first Words of the Year that works as an interjection – a burst of energy that spreads and connects people long before anyone agrees on what it actually means."The origins of "6-7" appear to stem from the song "Doot Doot," released by rapper Skrilla in December 2024.In the song, Skrilla sings, "The way that switch, I know he dyin'. 6-7. I just bipped right on the highway."According to Know Your Meme, a database for memes and internet slang, some people say "6-7" in the song is in reference to 67th Street, perhaps in Philadelphia, where Skrilla is from.Melina Khan is a national trending reporter for USA TODAY. Keep up with her on X @melinakh and Instagram @bymelinakhan.Greta Cross is a national trending reporter at USA TODAY. Story idea? Email her at gcross@usatoday.com.