A container (otherwise known as CT, Virtual Environment (VE), Virtual Private Server (VPS) etc.) is one of the main concepts of OpenVZ.
Container is an isolated entity which performs and executes exactly like a stand-alone server. Container can be rebooted independently and have root access, users/groups, IP address(es), memory, processes, files, applications, system libraries and configuration files.
OpenVZ allows to have multiple CTs (up to as many as several hundreds) on a single Hardware Node.