Virtual reality (VR) is the use of software and devices to simulate a 'real world' environment in which the user feels completely immersed. Often, this includes not just sight, but sound and gestures.
Watch this short video from GCFLearnFree.org to learn about virtual and augmented reality.
Virtual reality and augmented reality can be used for various forms of simulations and entertainment. Here are just a few examples of practical/educational uses: