OpenVZ is OS containerization like Solaris Zones or FreeBSD Jails. It is virtualization at the OS level whereby all containers share the same architecture and kernel version. It uses a single patched kernel called the Linux Containers (LXC) kernel.
Its one real advantage is that containers can be faster and more efficient compared with true virtualization because it does not have the overhead of a true hypervisor such as VMware or KVM.
Older versions of OpenVZ uses a common file system so each virtual environment is just a directory of files that is isolated using chroot as also occurs in Solaris zones. Newer versions can have different file systems.
Each container performs and executes exactly like a stand-alone server; a container can be rebooted independently and have root access, users, IP addresses, memory, processes, files, applications, system libraries and configuration files. However, if the common Linux kernel crashes, all containers crash.
OpenVZ comes with command line tools only. It forms the basis for the Parallels Cloud Server, a commercial virtualization solution offered by Parallels.