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There are two classes of reality experiences: casual and dedicated. The specifics depend on if it is for augmented reality or virtual reality.
For augmented reality experiences, dedicated would be a headset, like HoloLens. In this case, the user needs to wear a (currently) bulky headset to get a fairly small field of view of augmented information and/or experiences -- i.e., what you really see isn't as cool as the marketing videos. An AR casual experience is found with phone apps, where you open an app and point your phone's camera, with the augmented information showing up on the phone screen. This does not require a headset but is not as immersive -- and requires you to use your hand.
Virtual reality experiences are in a similar state. Dedicated, fully immersive experiences, like Vive, require you to wear a VR headset and fully remove your visual contact with your surroundings. You can mix reality with cameras, though, bringing some views of your actual physical environment into the virtual. But for most intents and purposes, you are cut off from your surroundings to provide better immersion. This has benefits and drawbacks depending on what you're trying to achieve. In addition, the Vive is a room-scale system, meaning the user can walk around. Other virtual reality experiences are designed for a user to stay in one place and locomote through some sort of physical interface, such as a hand-held controller. There have been experiments with treadmills and redirection in order to make small physical spaces feel as big as virtual spaces, but those are still not widely used -- or particularly good other than for a subset of experiences.
Casual VR is where your phone provides the computational power, and the VR experience is enabled by raising a relatively inexpensive viewer -- e.g., holding the phone -- to your face. It is "casual" in that you don't have a headset strapped on your head -- you can go in and out of the experience at will. It isn't as immersive as something like a Vive, but all virtual reality or augmented reality experiences are a set of tradeoffs among level of immersion, level of comfort, efficacy and so forth. Again, it depends on what you're trying to accomplish.