The simulation hypothesis proposes that what humans experience as the world is actually a simulated reality, such as a computer simulation in which humans themselves are constructs. There has been much debate over this topic, ranging from philosophical discourse to practical applications in computing.
Nick Bostrom in 2014
A simulated reality is an approximation of reality created in a simulation, usually in a set of circumstances in which something is engineered to appear real when it is not.
A researcher using a virtual reality headset, having entered the simulated reality of a lunar habitat.