Two whole new entertainment mediums have entered the world stage in the forms of Virtual Reality (VR) where users are transported into a virtual space through the use of a Head Mounted Device (HMD), and Augmented Reality (AR) where virtual elements are superimposed on top of a display showing the real world. For the sake of brevity, these two terms are often combined into the singular term XR. There is also the Mixed Reality (MR) (also known as Hybrid Reality or HR), where an application mixes the real and virtual worlds together, which encompasses all of previously mentioned formats, while also including Augmented Virtuality where real world objects are scanned and superimposed inside a mostly virtual world.
The markets for these media formats have sprung up very fast and are continuing to grow rapidly, with huge investments from the technology industry's biggest players. Naturally, Game Engines such as Unity jumped on the bandwagon...