OpenVZ is an operating system-level virtualization solution that allows multiple isolated virtual servers (containers) to run on a single physical host. Each container uses the common kernel of the host's operating system, but has an isolated file system, processes, network, and resource limits. OpenVZ containers are not fully isolated like in full virtualization, but they offer excellent performance due to the lower overhead since they share a single kernel instead of emulating separate virtual machines.
Thus, in this type of virtualization, all resources will be allocated to your project, while KVM virtualization requires a separate operating system installation, which also consumes resources and has minimum requirements.
This type of virtualization is perfect for web projects that do not need direct access to the operating system kernel. Only operating systems from the Linux family are available.
The operating system itself also has resource requirements, so it is important to consider them for your project. Its main advantage is complete isolation and direct access to the operating system kernel, which allows for running telephony-related projects, creating VPN tunnels, etc.
Here, you get all the advantages of a physical server, and it is also necessary to consider the system requirements for the operating system.