The hypervisor is a platform that sits on top of hardware resources the enables virtualization. The virtualization becomes the platform that allows the creation of virtual machines and the sharing of hardware resources.
There are different Hypervisors. You get hardware Hypervisors that consist of operating and hardware and installed in a system, and the VMware ESXi server is an example of this. The second type is software hypervisor, and its hosted on the OS of the VMware system that runs the VMware, an example of this is VMware Workstation professional.