For more details, see Introducing Oculus Quest, Our First 6DOF All-in-One VR System, Launching Spring 2019 (Oculus blog)
"That puts Quest squarely in the middle of Oculus’s other two headsets: the mobile Oculus Go, priced at $199, and the Oculus Rift, which also costs around $400 but requires a high-powered PC to use. But the Quest headset isn’t just the end result of a product differentiation strategy. It’s a showcase for potentially game-changing virtual reality technology, and part of Facebook CEO Mark Zuckerberg’s lofty goal to get 1 billion people using VR, as he expressed during the event's keynote address.Oculus’ $399 Quest to Take VR Mainstream -- Wired
The Quest hardware looks unremarkable from the outside, and it uses the same Touch controllers as the Rift. But there are four wide-angle sensors on the headset that are part of the technology that makes the Quest stand out. The Quest has six degrees of freedom—“6DoF” as it’s sometimes called—which allows your head to be tracked positionally, rather than just rotationally. In other words, you can move, not just look around."