In some cases, radio stations are considered legal where the signal is transmitted, but illegal where the signals are received—especially when the signals cross a national boundary. In other cases, a broadcast may be considered "pirate" due to the nature of its content, its transmission format (especially a failure to transmit a station identification according to regulations), or the transmit power (wattage) of the station, even if the transmission is not technically illegal (such as an amateur radio transmission). Pirate radio is sometimes called bootleg radio[1] (a term especially associated with two-way radio), clandestine radio (associated with heavily politically motivated operations) or free radio.