Simple definition
Nested virtualization allows a hypervisor to run inside a virtual machine when supported by the host and CPU.
Purpose and use
Nested virtualization allows a VM to run its own hypervisor and virtualized environments.
How does it work?
The outer hypervisor exposes required capabilities; availability depends on processors, versions and settings.
Example and verification
For a lab, verify exposed features and support before assigning resources to inner VMs.
Points to watch
Performance and selected networking or migration features may differ from a directly supported physical installation.
In short
A working nested setup does not automatically provide the same guarantees as native deployment.