Slang has been a thing for every generation, but thanks to social media, it spreads like wildfire for young people today—and dies just as quickly. (Remember when everyone was saying “cheugy”? Yeah, us too.) One day a phrase is everywhere, the next it’s painfully cringe. And if you’re someone trying to keep up, tween slang especially can feel like a completely different language. While some of their lingo overlaps with Gen Z’s, tweens have also carved out their own chaotic, often nonsensical vocabulary. Parents are confused, SNL has poked fun at it, and tweens themselves have turned school topics into...