What is Virtual Reality?

VR is the technology by with a head-mounted display teleports you in a virtual world by shutting out the outside real world.

VR

source: Marshmallowlaserfeast
in the eye of the animal

Virtual Reality was first imagined in Science Fiction and as many technologies that were once dreamed up are now real. Actually the very first version came up already in the 1950 with immersive film-viewing cabinets.
The technology relies on our eyes capabilities to have stereoscopic vision when two images that slightly differ in perspective are placed in front of our eyes. This is how a sense of depth and volume emerges.
Furthermore by tracking the position and rotation of the head when an observer wears a headset, the images that she or he sees are in correspondence with the direction of his head. This makes the observer feel as if she or he was in a different space.

let's live virtually

With virtual reality becoming more and more accessible it could fundamentally alter the way we communicate and interact. It can bring new ways to meet and connect with people, and can displace our need for physical travel which could in turn decrease energy consumption. It can enhance education by offering training from the first perspective (already widely in use) but also in the education of children, VR could offer to directly travel to another place and time and visualize events that took place, making education more vivid and memorable. VR can replace and/or extend retail stores. Also production costs can be cut by first testing prototypes virtually vs first using expensive resources to construct them and then discarding them. Buildings can first be visited before they are constructed giving a better feel and visualization of the outcome.
Games and cinematic experiences can be transformed by letting the audience be placed directly in the middle of the events, making the player and movie-goer part of the story itself. And many many more applications are possible.

 

Some things to the technical aspect.
Today there are many headsets available. The main difference between them is whether they are wireless (mobile device) or rely on wires and whether there is inside-out (so extra sensors required) or outside tracking (obnoxious sensors required).
Those relying on wires are directly linked to a GPU (vive, valve, oculus rift), they are annoying to wear at times when you stumble over the cables. There is a lot of plugging in and setting up before you can use them but the reward are really good graphics and performance. This means that a powerful gaming PC need to be available which is a drawback for many people. Many VR Experiences run only on GPU powered headset and they are generally the best experiences.
On the other hand there are wireless mobile devices. The oculus quest was the first one which had position tracking. As they are mobile, the graphics are not that good, but when a game or experience is well done the performance can be really good and being able to walk around freely without constraint is phenomenal. The cool thing about the quest is that in can now also be plucked into a gpu, giving you its full power.
Most other mobile devices (google cardboard, oculus go) don’t have position tracking and are only used for 360°.

Valve Index. source: valve
oculus quest. souce: oculus