Device Driver

A program that allows a specific device, such as a modem, network adapter, or printer, to communicate with the operating system. Although a device might be installed on your system, Windows cannot use the device until you have installed and configured the appropriate driver.
If a device is listed in the Hardware Compatibility List (HCL), a driver is usually included with Windows. Device drivers load automatically (for all enabled devices) when a computer is started, and thereafter run invisibly.