The entire electrical grid relies on the ground as a conductor. If your electrical outlet has two wires, one of them is connected directly to the literal ground via a metal post buried outside your home. If it has three wires, usually two of them are connected directly to the ground.
In most electrical systems one of those ground wires is also connected to a neutral wire that leads back to the generator. But there do exist "Single Wire Earth Return" systems where the neutral return wire is omitted and everything still works. https://en.m.wikipedia.org/wiki/Single-wire_earth_return
In most electrical systems one of those ground wires is also connected to a neutral wire that leads back to the generator. But there do exist "Single Wire Earth Return" systems where the neutral return wire is omitted and everything still works. https://en.m.wikipedia.org/wiki/Single-wire_earth_return