SPDIF - Sony Philips Digital Interface
its a co-axial type connector which looks similar to Phono cables, they carry a stereo digital signal. This signal requires a clock source to function correctly. In your situation its usually the soundcard which supplies this. They work at either 44khz or 48khz.
You could use it with anything else that has a similar connection. In my studio i use it to send the master bus audio to another computer which acts as a recording device and itself has a basic soundcard with SPDIF capability. It is noise free and simple and because its digital to digital i dont need balanced cables or even a very expensive soundcard. And advtange of this is that in some sequences im running close to the limit of CPU power and/or disc recording and if i try to bounce realtime by sampling from the master OP then i get drop outs or stalls of the audio engine.