Snakes are basically a number of
individual cables wrapped together within a protective metal
mesh which is then covered in a rubberised outer sheath.
They tend to come in standard configurations:
15m, 30m and 45m lengths
12, 16, 20, 24 cables
Typically the stage end is
terminated in a block with 4 XLR female connectors (bringing
back signals from the mixer) and the rest are XLR female
connectors (taking mike and instruments).
The mixer end reverses the
connectors but they terminate with loose cable and XLRs.
Then each cable is wired for
balanced use. However you can put un-balanced line signals
down them and you can use one cable for the stereo output of
a keyboard. In this case you would need a stereo jack socket
to XLR cable.