Dualview
A feature found on many laptop computers and some high-end display adapters that enables the user to display what is being shown on their laptop to be displayed on an external display device connected to the laptop, such as a monitor, flat-panel display, or projector. In addition many computers that support dualview can also be used it to extend the display horizontally or vertically.
Laptop computer users: Once an external display has been connected to a laptop that supports dualview mode, if the external display does not automatically start working you may have to press a function key on the laptop keyboard to enable/disable the dualview mode or to adjust it.
Also see: Projector, Video definitions