modem

 An electronic device that converts electronic signals into sound waves, and sound waves into electronic signals, used to transmit information between computers by the use of ordinary telephone lines; also called modulator-demodulator; as, the latest modems can transmit data at 56,000 baud over a clear telephone line. The speed of transmission of information by a modem is usually measured in units of baud, equivalent to bits per second.  [PJC]