AR, VR, Mixed Reality -- What's the Difference?

Maybe you're confused. I certainly have been and I work in this industry. There are a bunch of different acronyms floating around to describe how computers can be used to create images to represent a simulated reality. "VR" or virtual reality is just what it sounds like: a reality that is completely virtual. "AR" or augmented reality is "computer assisted reality". So, what is "mixed reality"?