Virtualization is the process of running a guest (such as an operating system) on top of virtualized/emulated hardware through the use of a hypervisor. This enables the concurrent execution of several operating systems on one piece of physical hardware. Potentially, this makes machine resource usage more efficient. Virtualization is also used to turn a server room of physical machines into an abstract "computing cloud", accessible through some unifying management framework.

See also Guest, Hypervisor, Full virtualization, and Paravirualization.