Facebook says there are 900,000,000 people who use Messenger on a regular basis. That's a lot of people, so Facebook has come up with a new way to make it easier to find someone. You now have the option of creating a Messenger username, which also works as a link or a scannable code.
Your username can be set in the Messenger settings tab, and once you do, others can add you at m.me/yourusername. That's handy for the web, but what about when you meet people in real life? That's where codes (accessible in your profile) come in. Facebook says it took great care to make the codes look nice, so they aren't just bland QR codes. They have a similar vibe, though. You will see a profile picture, and around that a series of dashes and dots. That's the unique identifier that others can scan by opening the "scan code" feature in settings.
Unlike some other features, this one appears to be rolling out for both Android and iOS starting today. I'm not seeing it in the Android app yet, but it'll probably be triggered by a server-side change.