Let's Clear-up the "MR" "Mixed Reality" Question...
I've been seeing a lot of people wondering about what MR/Mixed Reality is and how it fits-in with VR and AR.
MR, or Mixed Reality is simply a term coined by Microsoft, and they themselves explain what they mean by it:
Mixed Reality simply refers to the fact that Microsoft's VR (Virtual Reality) Headsets will work in conjunction with Hololens (and any other Microsoft Compatible AR/Augmented Reality Headset).
That's it. It's just a way of describing how a person with a VR headset will be able to collaborate on a project/game/design or anything else along with a person wearing an AR headset, either right next to them, or half-way around the world.