The kernel has a few virtualization subsystems:
- UML
- LXC
- KVM
Comparisons:
- https://unix.stackexchange.com/questions/90078/which-one-is-lighter-security-and-cpu-wise-lxc-versus-uml/93924#93924
- https://stackoverflow.com/questions/20578039/difference-between-kvm-and-lxc
Optionally used used by QEMU.