“Snake” is a generalized term for many cables all permanently bundled together in a tube or other binding. A snake is useful when you need to route a bunch of cables from one location to another — rather than running all the separate cables, you can run one snake cable, which saves time and often cable expense.
Sound engineers will very often have an audio snake that has either a series of XLR cables, or a multi-input box with many XLR jacks, placed on the stage, with the other end of the snake leading to the venue’s soundboard or PA system. But a cable snake can also be useful for musicians. If you’re a guitarist using the “four-cable method” to connect your pedalboard at the front of the stage to your amp at the rear of the stage, a snake allows you to run one cable instead of several. A keyboardist with a large stack of keyboards/synths could use a snake to route signals to his mixer or to front of house.
Normally snakes are used in the pro audio/music world to carry analog audio signals, but some also include MIDI and digital audio lines, and even AC power cabling for running pedalboards. Depending on the cable used to create the snake, it can be balanced, unbalanced, or a mix of the two, and can have any assortment of connectors required on each end — XLR, 1/4″, DB25, RCA, MIDI, and so on.