S/PDIF (Sony/Philips Digital Interface) is a standard audio transfer file format. It is usually found on digital audio equipment such as a DAT machine or audio processing device. It allows the transfer of audio from one file to another without the conversion to and from an analog format, which could degrade the signal quality.
The most common connector used with an S/PDIF interface is the RCA connector, the same one used for consumer audio products. An optical connector is also sometimes used.