TOSLINK is short for Toshiba Link, TOSLINK is a CD "Red Book" standard that allows for digital audio (both left and right channels or multi-channel sound) to be transported between components using an optical conductor and light as the carrier. Contrary to popular belief, TOSLINK does not use laser light but instead relies on the output of a simple LED. The Achilles heel of TOSLINK is the optical quality of the interface. The plastic conductors used in cheap cables can damage data and compromise performance.

TOSLINK connection performance is somewhat limited by the bend radius (bending a light conductor causes internal reflections and signal loss) of the conductor design. Additionally, the TOSLINK interface is length sensitive with maximum performance available only with runs of less than 20 feet.

TOSLINK, or more properly EIAJ optical, signals have exactly the same format as the electrical S/PDIF signals except, instead of using high/low voltages on copper to represent the binary 1's and 0's of digital information, TOSLINK utilizes a series of on/off pulses of a red transmitting light.

The optical interface of TOSLink and ADAT Lightpipe are not compatible with each other.