A feature supported by some notebook computers that enables them to display images on an external monitor at a higher resolution than is supported by the built-in flat-panel display. For example, most flat-panel displays are limited to a maximum resolution of 800x600. With the virtual desktop feature, you could connect the computer to an external monitor and enjoy full SVGA (1,024x768) resolution.
The term also refers to a feature supported by some video adapters that enables them to provide a desktop larger than what's actually displayed. Only part of the virtual desktop is displayed at any one time, but you can see hidden areas by scrolling the display. It's as if the display screen is a small window overlaid upon a larger desktop.