Recommended standard-232 (RS-232),
Definition of Recommended standard-232 (RS-232):
Older standard for serial (asynchronous or synchronous) data transmission between computers and devices (such as modem, mouse, plotter) which specifies electrical, functional, and mechanical interfaces. Officially known as EIA-232 (latest version being the EIA-232E), it does not specify the connector which has either 25-pins (called DB-25) or 9 pins (called DB-9) and may be wired differently by different vendors. A common RS-232 cable typically carries data at 20 kilobits per second (Kbps) speed, up to a distance of 50 feet (15.4 meters) which may be extended by the use of a higher quality cable and/or repeaters. Superceded by universal serial bus (USB).
Meaning of Recommended standard-232 (RS-232) & Recommended standard-232 (RS-232) Definition