Imagine you have a computer, and your friend also wants to use the same computer at the same time. But your computer only has one keyboard, one mouse, and one monitor - so how can both of you use it together?
One solution is to use multiseat desktop virtualization. Basically, this means you can make it so that your one computer becomes like two or more separate computers, each with their own keyboard, mouse, and monitor.
You can do this by creating multiple "virtual" computers within your one physical computer. Each virtual computer has its own "seat" - that is, its own keyboard, mouse, and monitor. This way, you and your friend can each have your own "virtual" computer to use at the same time, even though you're still sharing the one physical computer.
Multiseat desktop virtualization technology makes this possible by dividing up the resources of the physical computer and sharing them between all the virtual machines running on it.
Overall, multiseat desktop virtualization is a clever way to get more use out of one physical computer and make it possible for more than one person to use it at the same time.