OpenVZ is virtualisation at OS-level, which means the node's kernel is used, to split the OS into containers.
The kernel is shared between several VPS, rather than fully emulating it like KVM does.
This results in lower memory and CPU overheads on the host node. Users should see better CPU performance on OpenVZ as you get full access to the node processor.
Unfortunately it also means Windows and BSD operating systems are not supported, and custom kernels cannot be used.
If you need a simple Linux container, then OpenVZ will do the job for you at an affordable price.