RS-232 - the physical layer for asynchronous (UART) interface. Historically was widespread in telecommunications equipment for personal computers. Currently still widely used to connect all kinds of special equipment to computers, but actively displaced interface USB. 
RS-232 data transfer and some special signaling between the terminal and the communication device at a distance of 15 meters. 
RS-232 - wire full-duplex interface. Data transmission method similar to asynchronous serial interface, that is, converts the specified data set in serial form, so that it was possible to pass them on a single digital line to another similar device. 
The information is transmitted by wire from a binary signal with two voltage levels. Logical "0" corresponds to a positive voltage (+5 to +15 V for the transmitter) and a logical "1" is negative (-5 to -15 V for the transmitter). For electrical matching lines RS-232 standard digital logic UART chip manufactures a wide range of drivers, such as MAX232.