What is this?

It's for an accessory you don't have on your model.
They pretty much built one harness for all models, then plug the ends of the
models that don't get certain items.
It's costs them less, saves time, and they only have to keep ONE harness in stock.

 

How they manage the wire harness inventory is kind of on a continuum ... they can use techniques like that to reduce the number of different harnesses they build, but they don't always reduce it down to one. There are definitely variant harnesses used between the different trim levels, and you can see the differences by looking for the little numbered * symbols in the wiring diagram. That's one of the things that can be a real headache when trying to add an accessory from a different trim level ... often the wires aren't there.

In this case, it looks like they did provide the wires for some accessory you haven't got.