closed circuit

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

• noun An electric circuit providing an uninterrupted, endless path for the flow of current.
• noun A television transmission circuit with a limited number of reception stations and no broadcast facilities.

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

• noun A complete electric circuit around which current can flow.
• noun A network of one or more television cameras and television receivers connected together with no provision for broadcasting.

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

• noun a complete electrical circuit around which current flows or a signal circulates