You may not have time to learn everything there is to know about virtualization, but a familiarity with the terminology will help you follow the trends, technical details, and industry developments as they emerge. Here’s a quick rundown of the virtualization terms you’re most likely to encounter.

Virtualization is one of the hottest topics in IT these days, but the technology brings with it new terminology that can be confusing. Here are some common virtualization-related terms and their meanings.

Note: The complete glossary is available as a PDF download.

#1: Bare metal hypervisor

Virtualization platform that runs directly on the hardware and does not require a separate host operating system. Examples are Hyper-V, ESX Server, and Citrix XenServer.

#2: Child operating system

Another term for the guest operating system that runs in a VM on top of the parent or host OS.

#3: Fully virtual

A VM that completely emulates all hardware devices.

#4: Grab

To direct the input of your keyboard, pointing device, etc., into a virtual machine (usually by clicking in the VM’s console window).

#5: Guest clustering

Clustering of virtual machines within the same node (a shared SCSI adapter) or across different nodes (iSCSI or fibre channel SAN).

#6: Guest operating system

An operating system installed in a virtual machine.

#7: Hardware assist

Technology by which the computer’s physical processor allows software to specify instructions to make those instructions virtualizable and take advantage of offloading to system hardware. Intel’s VT and AMD’s AMD-V support hardware assist.

#8: Host operating system

The base operating system installed on a physical machine, on top of which the guest operating systems are installed in virtual machines, and which interacts with the hardware.

#9: Hosted hypervisor

Virtualization software that runs on a host operating system and on which virtual machines run. Examples are Microsoft’s Virtual PC and Virtual Server, VMWare’s VMWare Server (formerly GSX Server), and VMWare Workstation and Parallels Desktop.

#10: Hypervisor

A virtualization platform that enables running multiple operating systems on the same physical computer, also known as a virtual machine monitor (VMM).

#11: Snapshot

An image of the state of a virtual machine at a specific point in time that includes all the data plus the configuration information for the VM, to allow you to return to that state in the future after changes have been made.

#12: Soft ungrab

Automatic switch of input from the VM to the host OS, as when the pointing device’s pointer moves out of the VM window.

#13: Synthetic devices

A new concept in Hyper-V that provides a lower overhead for devices than emulated devices.

#14: Unity

In VMWare, a viewing mode whereby applications running on the guest OS appear as application windows on the host OS desktop as if they were running on the host OS.

#15: .VHD

Virtual Hard Disk; the file format used by Microsoft for a file that holds the data on disk for a specific VM (guest or child operating system and the applications installed on it).

#16: Virtual appliance

A virtual machine with a fully preinstalled and preconfigured OS image, usually hosting a single application.

#17: Virtual hardware emulation

Software implementations of hardware devices that may be mapped to the computer’s physical hardware devices.

#18: Virtual machine (VM)

A software implementation of a computer that behaves like and appears to the network like a separate physical machine, but that can be one of multiple virtual machines running on the same physical machine.