In historical terms, a temporary physical connection secretly placed on a metallic circuit in order to monitor the information being transmitted across it. In contemporary terms, a wiretap need not be a physical connection on a circuit, but can take many forms, including the interception of a radio signal. In the United States and many other countries, wiretaps are illegal unless authorized by court order, or perhaps the order of a federal agency or of the executive branch of government in times of war or in the interests of national security. See also eavesdrop and Echelon.