A driver is a small piece of software that tells the operating system and other software how to communicate with a piece of hardware.
For example, all printers come accompanied with drivers to install that tell the operating system exactly how to print information on the page. Sound card drivers tell your software exactly how to translate data into audio signals that the card can output to a set of speakers. The same applies to video cards, keyboards, monitors, etc.
The drivers for each piece of hardware in your computer are centrally managed from Device Manager, available in all versions of Microsoft Windows.
