An Hypervisor is a software that allows several operating systems to share a single physical host. It’s also called Virtual Machine Manager and manages the distribution of the computational resources between the installed virtual machines so that the behaviour of the single guest operating systems is completely transparent with respect of the underlying physical hardware.

There two kind of Hypervisors: type-1 -also called bare-metal- which are directly installed on the host (such as ESXi, Hyper-V, XenServer and Proxmox) and type-2, called hosted. In this case software is installed as an operating system level application (like VMware Player, VirtualBox, etc).