1. To stop a telephone call directed to an improper, disconnected, or restricted telephone number, and to redirect that call to an operator or a recording.
2. To gain possession of communications intended for others without their consent, and, ordinarily, without delaying or preventing the transmission.
Note: An intercept may be an authorized or unauthorized action.
3. The acquisition of a transmitted signal with the intent of delaying or eliminating receipt of that signal by the intended destination user.
Source: from Federal Standard 1037C and from MIL-STD-188
See also Interceptor aircraft.