I'll be the pedant then and say that how I understand it is that AR is just adding things, VR is when it replaces things entirely, MR is more than AR because there are digital and physical elements to interact with. XR, then, is an umbrella term that encompasses all of the above. Spacial computing vs XR as the phrase to use? Sure.
How I understand it:
VR is an entirely artificial environment.
Augmented Reality is a mix between real world and artificial elements, in any proportion.
Mixed Reality is Microsoft's term for AR.
Spatial Computing is Apple's term for AR.
