KVM stands for “Kernel-based Virtual Machine” which is a virtualization module baked into the Linux kernel. As long as the hardware has Intel VT or AMD-V enabled, it means the computer/computer server running the latest version of Linux can easily run one or more “full virtualization” virtual machines using KVM. Each virtual machine (VM) has it’s own private hardware, including networking, disk, and more.
OpenVZ only offers OS-level virtualization, meaning they use the host operating system’s (the host OS is the one running directly on the physical hardware) kernel. These are therefore a container-based system, and you may only run Linux operating systems on an OpenVZ container since it relies on the host kernel.