A wire harnes is a set of wires that has all the conductors needed and can just be installed into something. There's a wiring harness in your car. They don't install the wires one-by-one. A harness is built for the product and is installed like any other part. There can be many branches on a wiring harnes to go to different places in the product. There may be more than one harness. There could be one for power, one for communications, etc. This is more efficient than installing separate wires.
