Final answer:
A double-insulated power tool provides two layers of insulation to protect the user from electrical shock, with a non-metal exterior to prevent current conduction.
Step-by-step explanation:
A double-insulated power tool is a device that has been designed with two separate layers of insulating material to protect the user from electric shock. Unlike tools with an earth connection, the double insulation provides a barrier which prevents electrical current from being conducted to the user, even if one layer of insulation fails. Double-insulated tools typically do not have a metal exterior and instead use a non-conductive material such as plastic to further reduce the risk of shock.