1. Low-level software that provides an interface between Operating System and the hardware devices. A driver exists to allow for device-independent applications. From time to time, drivers must be replaced whenever a new or updated application is installed.
2. In hardware, a circuit that provides input to another circuit. It is usually termed a preamplifier, or preamp.
3. The big gun in your golf bag.
4. Often, a loose nut behind the wheel.