I think the best definition has been provided by Milgram and Kishino defined a mixed reality as "anywhere between the extrema of the virtuality continuum", where the virtuality continuum includes on one hand physical reality, and virtual reality on the other.

Hi, 

Apart from the virtuality continuum that Andrea already mentioned you might look at the Pine & Korn "Multiverse" (Pine II, B. Joseph, and Kim C. Korn. Infinite possibility: Creating customer value on the digital frontier. Berrett-Koehler Publishers, 2011.).

They extended the virtuality continuum with an extra dimension ''Matter" thus arriving at 8, not 4 forms of mixed realities. 

Deleted research item The research item mentioned here has been deleted

I found this framework to be quite useful as a generative framework in the conceptualization of mixed-realities experiences (e.g. in the project mentioned in the attached position paper). 

My2Cents

Conference Paper Two countries, eight museums: aiming for cross-cultural expe...

As Andrea stated above and understand that Augmented Reality and Virtual Reality are both types of Mixed realities that are on opposite ends of the spectrum or the virtuality continuum .  

Note: Some would say that virtual reality is not necessarily a mixed reality but I argue that it is nearly impossible  to completely simulate virtual world without some kind of neural interface similar to what was used in the film The Matrix.

Augmented Reality (where a virtual interface overlays the physical world--such as using a QR code to see more information about a physical object or space) is one example, but another example is a human-in-the loop interface. For example, you could have avatars (computer animated characters controlled by people) that interact with people in a simulated training. 

Interactive systems in which the human perception of the world is mixed with synthetic stimuli that can be generated on real time. As opposed to VR, mixed reality does not block sensory channels from the world. As opposed to AR, mixed reality doesn't require hand-held or wearable interfaces. Example: El Ball del Fanalet (Lightpools) by Perry Hoberman & Galeria Virtual (Narcís Parés & Roc Parés)  https://vimeo.com/157922712

I second the answers of Andrea and Koen. I think I saw a definition somewhere lately that put mixed reality between simulation (of real environment) and 'virtual' reality (completely make-believe fantasy environment), but I'll have to check the source, can't recall it right now.

It is interesting that I've read more cohesive net of answers here than I heard during the ITEC/17 conference.

Let me update this with some notes I had during the ITEC/17 conference, on Military Simulation, but that can be easily applied to other simulations as well. I heard a few opposing ideas and concepts all over the event (wich is good, for questioning is the first step after the answer) and I would like to share some of them with you:

1) Dr Tom Killion, NATO's Chief Scientist, pointed out that we already live in a Mixed Reality environment, since we are constantly shifting our senses between the real world and virtual worlds [I would say pieces of a loosely connected Metaverse]. He used the example of navigating with the help of Google Maps.

2) On the other hand, Denis Potapenko, CTO on Program ACE, stated that Hololens is a Mixed Reality system, instead of a Augmented Reality device.

Those are interesting views, but analyzing all the definitions I've heard and read, I was able to put them under this classification:

-Augmented Reality: systems that overlay the users view of the real world with virtual images and data, without total occlusion of the real surrounding environment.

-Virtual Reality: systems that immerse users in a totally virtual environment, with the main objective of creating an experience of disconnection between the user and the real world.

-Mixed Reality: systems that immerse users in a totally virtual environment, but maintaining a connection with the real surrounding environment by synchronizing them in some way by sensory stimulation.

Therefore, I would say that Google Maps is, indeed, a Mixed Reality application, but that is not true for any apps, just because one can shift his/her attention between both worlds, virtual and real.

Regarding the Hololens, the first presentations I saw made me think of it as an AR device; but after experimenting it, I'm not so sure anymore. May be it can do both things (AR and MR) depending on witch features the developer will use. I'll have to dig in a bit more on the Hololens before I can state something.

For a definition of Mixed Reality I also understood it to be anything between completely real and completely virtual, as defined by Milgram and Kishino in the paper given in Andrea's answer above.

Concerning Augmented Reality, I have always found one of the points in the definition by Azuma et al (1997) important, that is missing from Carlos' definitions: In AR there is a combination/relationship between real and virtual elements. So as an example, an overlay display like Google Glass would fall in the category of Mixed Reality rather than Augmented Reality, because the content that is displayed is independent from the real objects that are looked at in the surrounding environment.

I share the same concern with you. However, per my readings I am tempted to think it is virtually the same as augmented reality (AR). Experts are just massaging vocabularies.

I found this link very helpful: http://www.realitytechnologies.com/mixed-reality

https://www.foundry.com/industries/virtual-reality/vr-mr-ar-confused

Adding to the answers above, some applications (mostly early days Unity games like Audioshield) use the term Mixed Reality or Mixed Reality Capture to describe rendering the game world ontop of a camera feed filming a player (infront of a green screen).T he cameras position is tracked in render/game space.

https://developer.oculus.com/documentation/unity/latest/concepts/unity-mrc/

There is not a single, "best" definition of MR. In fact, my colleagues and I investigated this question for a paper presented at this year's CHI conference. Based on expert interviews and a literature review, what we found were 6 distinct and widely used working definitions:

• MR according to Milgram's continuum
• MR as a synonym for AR
• MR as a type of collaboration
• MR as a combination of AR & VR
• MR as an alignment of environments
• MR as a "stronger" version of AR

These can be classified based on a conceptual framework (some would call it a taxonomy) with 7 dimensions:

• number of environments
• number of users
• level of immersion
• level of virtuality
• degree of interaction
• input
• output

Hope this helps! :)

Mixed reality term was coined in the late 80ies and 90ies simply referring to semi-immersive VR, which is doing VR using a mix of completely immersive (e.g. hmd) and not immersive (e.g. using a computer display) approach. AR did not exist at that time. Someone has appropriated of this term later (e.g: wikipedia, Milgram's continuum) to referr to other meaning. I think the question should be: is AR a not immersive VR approach, a mixed VR approach or is it a completely immersive VR approach (could be a mix of them)?

Nice Contribution Luiz Marcos G. Gonçalves