OpenVZ

NOTE: OpenVZ is supported until Proxmox 3.4 and will end with Debian Wheezy security updates (expected end in April 2016)

OpenVZ is container-based virtualization for Linux. OpenVZ creates multiple secure, isolated containers (otherwise known as VEs or VPSs) on a single physical server enabling better server utilization and ensuring that applications do not conflict. 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.

Currently all Proxmox VE Appliances are OpenVZ based and are "production ready".

For details see OpenVZ.