TOSLINK or Optical Cable is a fiber optic connection system. Most commonly used with audio equipment (via a "digital optical" socket,) where it carries a digital audio stream from devices such as CD, DVD, Blu-Ray players and modern video game consoles, to an AV receiver such as surround sound system that can decode the stream of audio and output it through a set of loudspeakers.
Since TOSLINK uses fibre-optic cable, it is free from distortion caused by electrical or magnetic interference that an electrical cable would incur.
The result is an audio signal that is purer, as well as truer to the original recording. Gold plating is used on the connectors for its anti-corrosive properties.