Toslink is a digital audio connector that transmits sound with light and with a single connector can transmit 7.1 sound, instead of with 3 connectors. 

This connector is low for connecting a digital system to a Mac, an Airport express (yes, it also has digital audio). 

All Mac's have digital sound, they just use the normal Mini Jack connector to transfer the light to the digital sound. 

The cable is very thin and light and it is made so it weighs as little as possible, the cable is made with plastic inside, this plastic must not be broken as it may happen that the cable cannot transmit sound after it.

As I said, all Mac's and airport expresser have digital sound, but there are also many other devices that have, our own Soundmate, which gives airplay to your plant has eg. Airplay can transfer sound in 5.1 to your airplay speakers.

We also have a normal Toslink cable, with Toslink at both ends: Toslink Digital Audio Cable 3m