driver: n.

1. The main loop of an event-processing program; the code that gets commands and dispatches them for execution.

2. [techspeak] In device driver, code designed to handle a particular peripheral device such as a magnetic disk or tape unit.

3. In the TeX world and the computerized typesetting world in general, a program that translates some device-independent or other common format to something a real device can actually understand.