Virtual Reality (Often abbreviated as V.R.) is an artificially controlled existence created by an intelligent species. Types of virtual reality can be categorized with the following system.
A Level 0 virtual reality is the bare bones of all VR. The first iterations of these can come in with things like stereoscopy, theatres with seats that move along with the screen and surround sound.
Other examples can be large machines that display images or videos. There could be parts of the machine that let certain smells and sounds out, making it as real is it can.
This is similar to the 1950s CE Earth VR.
A Level 1 virtual reality is very similar to your average video game, with the controller being able to completely control a character in their respective program using a type of controller apparatus. The suspension of control can be enhanced with the use of headsets wherein the person can turn their heads and the character's view would follow. And motion controls, allowing for the illusion of full hand movements.
This is similar to the 2010s CE Earth VR.
A Level 2 virtual reality is an upgraded version of a Level 1 one. It allows an individual to experience scripted and specifically programmed scenarios with full freedom of movement, as well as sense of touch, and smell. These would usually require the use of an entire room to operate, and are typically used for medical training, as well as military roles though this can vary depending on the species in question.
This is similar to the 2030s CE Earth VR.
A Level 3 virtual reality is a program that can update itself in real-time to the controllers' actions within it, allowing for full free form conversations and reactions from simple A.I. As well it has full freedom of movement, sense of touch, smell, and even pain if the user chose this. They are also much more compact, using simple bodysuits instead of entire rooms. Some species use it as a method of torture.
This is similar to the 2050s CE Earth VR.
A Level 4 virtual reality is a program that can extend itself endlessly and constantly, allowing the user to explore it without any form of limitation. As well, the user can completely customize it to their liking, making every one tailor-made to the user's wants. These are the most common virtual reality systems used by most intelligent species and are typically generated in small isolation chambers.
This is similar to the 2150s CE Earth VR.
A Level 5 virtual reality is a program that is completely indistinguishable to actual reality, making the controller's brain believe that this isn't an artificial universe and instead is the real one. For this reason, many civilizations, such as humans, have outlawed the use of these as they fear that this could halt progress indefinitely.
Certain species in the known universe have placed themselves within Level 5 virtual realities, with them living out their perfect lives instead of living in the material universe.
Some civilizations use Level 5 virtual realities as a humane way of imprisonment.
A Level 6 virtual reality is an entire infinite simulated universe, complete with its own intelligent species indistinguishable to actual life. These are typically used as experiments to see how a universe made up of countless civilizations operates through a god's eye view.
These are the most advanced known form of virtual reality, to the point that theories exist that the main universe itself is a Level 6 virtual reality.
The ethicality of these is often debated quite heavily by intelligent species, as creating entire universes with all of the nuances of life can be viewed as an immoral act, and the act of playing God can also be viewed as unhealthy.