Servers and hosting
KVM (Kernel-based Virtual Machine)
The virtualisation built into the Linux kernel. Each VPS is a real virtual machine with its own kernel, not a container sharing the host's.
KVM turns the Linux kernel into a hypervisor: each virtual machine gets virtual CPUs, memory and devices backed by the processor's hardware virtualisation, and runs its own kernel on top. The guest can be any operating system, Linux, FreeBSD or Windows, with its own kernel modules, firewall and filesystems.
That is the difference from container-based VPS (OpenVZ, LXC), where every "server" shares the host's kernel and is really an isolated process tree. Containers are lighter, but you cannot change the kernel, load modules, run a different OS, or count on the memory you were sold when the host is busy.
For a VPS, KVM means you can install from an ISO, run Docker or WireGuard without workarounds, and treat the machine like physical hardware. Memory and CPU limits are enforced by the hypervisor, so a neighbour cannot take yours.