I love acronyms, but these are a mouthful.
- S/PDIF (Sony/Phillips Digital Interface)
- TOSLINK Toshiba Link
- AES3 or AES/EBU Audio Engineering Society/European Broadcasting Union
The standards were co-developed for the consumer / professional markets. They define both the data transmission formats as well as the connectors and cabling used to connect devices to transfer digital audio. These standards include stereo and multi-channel audio formats.
There is some complexity in cable designs.
In AES3 the first is a balanced connection using the XLR connector. The second is an unbalanced connection using 75-ohn BNC connectors and cable. The third is TOSLINK.
S/PIDF uses an unbalanced connection with RCA connectors and TOSLINK.
The TOSLINK standard defines fiber-optic connectors and cabling for both the professional and consumer designs. There is a second connector standard called Mini-TOSLINK fits into a 1/8in audio jack where the emitter and sensor are at the tip of the connector.
NOTE: TOSLINK is not the same standard as computer networking optical cabling. It just happens to use a similar fiber-optic cable.
These connections are subject to some of the same issues that USB has. There are both clocking and jitter issues and like USB cabling matters.
Here are some Wikipedia articles to take you further.