Virtual machines are machines that use virtualized hardware. When compared to Containers, they provide better isolation (because the kernel isn’t shared with the host) but usually have more resource overhead.
In Linux, the typical stack is to use KVM as the underlying Kernel virtualization infrastructure and QEMU to emulate devices and piece things together into a VM. We can use libvirt as a common interface to abstract QEMU-specific logic. Most of the time, those VMs are managed by an Orchestrator such as Openstack, Incus or even Kubernetes with KubeVirt.
References
Linux Hypervisor Setup (libvirt/qemu/kvm)
https://documentation.ubuntu.com/server/explanation/virtualisation/vm-tools-in-the-ubuntu-space/