What is the difference between an impact driver and a regular drill?

Drills are used to bore holes. Impact drivers are specialized to drive fasteners, such as screws, into solid materials. The impact driver will use the rotational force provided by your cordless or electric drill, and combine it with high levels of torque, to provide bursts of impact. While the best drills can also be used for rotational force, an impact driver provides that drill + driver action to give you a powerful handheld machine.