A multiple conductor cable is a cable that has contained within its outer sheathing multiple smaller individual conductors or wires, all independent of the other conductors. Each wire is electrically isolated from the others. 

A commonly known cable that has multiple independent conductors found in most homes is telephone wire or Cat 5/5e/6 cable.  The benefit of having multiple conductor cables is that by running or routing one cable you now have access to several independent conductors. Not only is it cheaper to have one multi-conductor cable, but it is also a lot more concise and easier to use.

It is often used when several conductors are needed for a system to work, and several different signals have to travel to similar locations but can’t share the same conductor.   Using the multi-conductor cable allows one to separate each conductor and electrical signals can be placed on each conductor individually eliminating any signal corruption, assuming the signals are slow in speed.

Multi-conductor cables are good for slow speed or power distribution and delivery. If high-speed signals are present on the individual conductors - there should be a corresponding signal, which is tightly twisted with it to make them behave as a pair. This is how a category 5 cable is wound and designed, which facilitates the ability to send higher speed signals on the conductors.