Virtual reality is the creation of a completely virtual world where viewers and users cannot tell what is real or not (as opposed to the use of augmented reality, that overlays virtual onto reality), creating a fully immersive experience. It requires the use of a headset.
We have space in the computer which is 100% CGI and Virtual Reality helps to explore that space - look up, look down, move around, and see what you want to see, when you want to see it. Virtual Reality allows viewers to see developments that are still in the planning process, imagining a world for the user to see what the property will be like.
Great for focused subjects but if you have a large design such as a public realm, the danger is the viewer may not explore the key elements of your design.
See also: Augmented Reality