extension cord

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An insulated, flexible electric wire fitted with a plug at one end and one or more outlets on the other, allowing one to plug in devices whose cords are not long enough to reach a wall outlet.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun electronics An electrical cord with a plug one end, and a single socket or a multi-port socket at the other end, used for powering one or more devices at a distance, too far from the wall outlet to be reached by the normal cords of the device or devices. (slang: trip cord).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an electric cord used to extend the length of a power cord