Virtual Private Servers
A virtual private server (VPS) is a virtual machine sold as a service by an Internet hosting service. A VPS runs its own copy of an operating system, and customers have superuser-level access to that operating system instance, so can install almost any software that runs on that OS. For many purposes they are functionally equivalent to a dedicated physical server, and being software defined are able to be much more easily created and configured. They are priced much lower than an equivalent physical server, but as they share the underlying physical hardware with other VPSs, the performance may be less, and may depend on the workload of other instances on the same hardware node.
KVM (Kernel-based Virtual Machine) is a virtualization infrastructure for the Linux kernel which turns it into a hypervisor. KVM requires a processor with hardware virtualization extension.
Xen is a hypervisor using a microkernel design, providing services that allow multiple computer operating systems to execute on the same computer hardware concurrently.
OpenVZ (Open Virtuozzo) is an operating system-level virtualization technology based on the Linux kernel and operating system. OpenVZ allows a physical server to run multiple isolated operating system instances, called containers, virtual private servers (VPSs), or virtual environments (VEs).