General Impact Screwdriver

Wikipedia on Impact Screwdrivers

From Wikipedia:

These are not to be confused with the impact wrench, which is a motorized tool (usually powered by compressed air), with a similar name and function. These also use a rotary hammering action to apply torque to fasteners. The difference is that impact wrenches do not provide the positive engagement that impact drivers offer as mentioned above. Otherwise impact drivers and impact wrenches operate in essentially the same fashion.