OpenVZ (Open Virtuozzo) is an operating-system-level virtualization technology based on Linux OS. It allows a physical server to run multiple operating system instances called containers, Virtual Private Servers (VPSs) or Virtual Environments (VEs).
Each container performs and executes exactly like a stand-alone server which means that a container can be rebooted independently and have root access, users, IP addresses, memory, processes, files, applications, system libraries and configuration files. OpenVZ uses a single Linux kernel and therefore can run only Linux.
All OpenVZ containers share the same architecture and kernel version. OpenVZ follows soft memory allocation which allows the efficient management of memory allocation where the unused memory in one virtual environment can be used by others or for disk caching. Because OpenVZ uses a single patch Linux kernel, but since it doesn’t have the overhead accompanied with legitimate hypervisors, it’s super-fast and extremely efficient.