Line level audio is an audio signal before
it is amplified to drive a speaker. Typical line level audio connectors include the RCA connector and 1/8 inch (3.5mm) plug & jack. Less common connectors include the 2.5mm jacks, 1/4" jacks, and specialty jacks like XLR.
Digital audio signals are carried over Toslink Fiber optic cable, and digital audio cable (which uses a standard F connector.)