In 1994 Paul Milgram conceived for the first time the Reality Virtuality Continuum, also called Milgram’s Continuum in a scientific paper where he (among with other colleagues) tried to describe all possible combinations of reality and computer-generated images in HUDs.
At the far left, there is the real environment, unmodified as our eyes see it. At the opposite side of the continuum, we can find the virtual environment where all that wee see has been generated by a computer. This is the case for VR headsets like Oculus Rift, Samsung Gear VR, HTC Vive, etc.
The area between the real environment and the virtual environment represents the mixed reality, with various degrees of overlapping between reality and virtuality.
Devices like Vuzix, Epson Moverio or Glassup F4 fall into the Augmented Reality case, where the virutality augments the reality (i.e. the virtuality is less relevant than the reality), whereas the Augmented Virtuality is represented by devices like Microsoft Hololens or Daqri helmets.
Now, imagine you are in a club and you see a very nice boy (or girl — hey, we embrace diversity here!) but you don’t know what is the perfect first approach: now you know the MIlgram’s Continuum.
You are welcome.