A host virtual machine is the server component of a virtual machine (VM), the underlying hardware that provides computing resources to support a particular guest virtual machine (guest VM).
The host virtual machine and the guest virtual machine are the two components that make up a virtual machine. The guest VM is an independent instance of an operating system and associated software and information. The host VM is the hardware that provides it with computing resources such as processing power, memory, disk and network I/O (input/output), and so on.
A virtual machine monitor (VMM) or hypervisor intermediates between the host and guest VM, isolating individual guest VMs from one another and making it possible for a host to support multiple guests running different operating systems.
A guest VM can exist on a single physical machine but is usually distributed across multiple hosts for load balancing. A host VM, similarly, may exist as part of the resources of a single physical machine or as smaller parts of the resources of multiple physical machines.