From The Jargon File (version 4.4.7, 29 Dec 2003):
virtual
adj.
[via the technical term virtual memory, prob.: from the term virtual image
in optics]
1. Common alternative to logical; often used to refer to the artificial
objects (like addressable virtual memory larger than physical memory)
simulated by a computer system as a convenient way to manage access to
shared resources.
2. Simulated; performing the functions of something that isn't really
there. An imaginative child's doll may be a virtual playmate. Oppose real
.