On the other hand, it is different because the "terminals" (or seats, as they are known in multiseat jargon) are composed of nothing more than the regular keyboard, monitor and mouse, and these devices are plugged directly into the PC.
USB hubs can be used for cable management of the keyboards and mice, and extra video cards (typically dual or quad output) may need to be installed.
Server based computing has been around for a long time specifically to take advantage of this excess CPU power and allow multiple users to share it.
Virtualization is a method by which the "guest" operating system runs on top of, while being separated from the "bare metal" hardware.
Although it is still server based computing and relies upon a "thin" or a "fat" client to display the video output of the session, it allows multiple users to launch the same application because they are launching totally different instances of the same application, in different "guest" operating systems.
Multiseat desktop virtualization is an entirely new methodology which combines the cost saving benefits and ease of maintenance of server based computing, the time savings of hardware agnostic cloning, and the capabilities of desktop virtualization, with the performance capabilities of real PC functionality.