In computing, virtualization (alternatively spelled virtualisation) refers to the act of creating a virtual (rather than actual) version of something, including virtual computer hardware platforms, storage devices, and computer network resources.
This article is the last in the mini-series and is probably the most contentious, not for any technical or philosophical reasons, but rather for the cultural divide which determines which side of the fence you sit on.
Usability is probably the most difficult concept to define when talking about virtualisation and particularly OpenVMS and virtualisation.