“Alesis Digital Audio Tape” or ADAT was pioneered by Alesis to simultaneously record eight tracks of digital audio at one time. The ADAT lightpipe protocol was developed to stream eight channels of 20 or 24 bit audio over an optical cable at 44.1kHz or 48kHz to allow for digital transfers between ADAT digital recorders. Today “ADAT” is used as the standard abbreviation for the ADAT lightpipe protocol and is still used to transfer eight channels of digital audio over a single fiber optic cable. The ADAT digital interface has been adopted by many audio manufacturers as a compact way to transfer digital audio data between devices. Devices ranging from consoles to synthesizers are equipped with ADAT I/O.
ADAT optical uses the same type of optical cables as the TosLink two channel protocol. These cables can be purchased at your favorite local recording store.
For a little history on how ADAT came to be, consider looking at this article on the web:
http://en.wikipedia.org/wiki/ADAT