RS-232 and RS-432 are two standards for serial connections from computers to peripherals. The standards specify the cable type and connector configurations. "RS" stands for "Recommended Standard."
RS-232 was defined in 1962 by the Electronics Industry Association (now the Electronics Industry Alliance). Control of the standards definition was passed over to the Telecommunications Industry Association in 1988. Since then, standards documents relating to RS-232 are referenced by the code "TIA." The standard is currently known as TIA-232-F. RS-432 was a faster version of RS-232 but was not widely adopted.
The standards specify the type of cable, the format of connector and the pulse rate and voltage levels for communications between computers and peripherals. Modems and printers are typical examples of implementation of RS-232 connections.
RS-432 was implemented in Apple Mac computers and the Enterprise 64 and 128 models. All other hardware manufacturers stuck with RS-232. These connectors have been superseded by the Universal Serial Bus (USB), and so modern computers only include serial ports for backwards compatibility.