science usually sees a system as a closed contraption, not able to exchange anything with the environment it lives in. However, systems in nature are mainly open rather than closed. We may see the Earth as such a system, but on the larger scale of things it gets its energy from larger systems like the solar system, the Milky Way, or ultimately the Universe. And even beyond that there may still be greater systems which have their own frame of reference.
Systems may be localized or distributed, contained in a larger system or spread out: the low voltage system of a car is complex and has lots of wires, but it can be simplified into a few controllers with hardly any wiring. Signals don't need a wire per signal perse, but can be serialized onto one wire, or even made wireless and duplexed onto their own channels.