A device driver is a specialized software program that allows the operating system to communicate with hardware devices, such as printers, graphics cards, and keyboards. It acts as a translator between the hardware and the software, ensuring that commands from the operating system are correctly understood by the device. When a new hardware device is connected to a computer, the appropriate device driver must be installed for it to function properly. Without the correct driver, the device may not work at all or may not perform optimally. Device drivers are essential for the smooth operation of hardware components in a computer system.