This document discusses virtual reality, including its history, types, hardware, applications, and advantages/disadvantages. Virtual reality involves computer-generated 3D environments that allow users to interact with simulated realities. The development of virtual reality began in the 1950s. There are three main types: immersive VR which provides full immersion, non-immersive which uses large displays but doesn't surround the user, and window-on-world which displays 3D environments on regular displays. Common VR hardware includes input devices like wands and gloves and output devices like headsets. Applications of VR include military training, healthcare, education, scientific visualization, and entertainment. Advantages are realistic experiences and experimentation, while disadvantages are high