Ground / Grounded / Grounding
In reference to electrical wiring, ground means to have a pathway to the earth. The term ground is synonymous with earth. The term ground is used in the US and the term earth is used in the UK. Home electrical systems are grounded using long rods driven deep into the ground or the home electrical system can be grounded to a cold water pipe that travel deep into the earth.
The term ground comes from the early use of lightning rods, pioneered by Benjamin Franklin. Lightning rods will run from the highest part of a building running down into the earth. So if lightening does hit, more than likely, the electrical current will flow through the rod to the ground, hence the term ground.
In reality, when lightning strikes, 90% of time the current flows from the ground upwards. Even today many homes rely on a rod pushed into the ground in the base of the house for its path to the ground.In reference to automobile wiring, here's a snippet from Matt Strong's book, "Custom Auto WIRING & ELECTRICAL":
In automobile wiring, ground is the term used for the electrical return in any automotive circuit. In houses electricity it is different, because AC circuits need two wires to conduct electricity while cars use DC, which is always running from positive to negative. The negative is called the ground because it does not generally have a separate wire: it uses the chassis and engine to complete the circuit back to the battery. Consider this: there is only one wire for each spark plug. The positive lead is from the plug wire. After the current jumps to make a spark, the return of the circuit runs through the engine block, the engine ground strap, chassis and finally back to the negative terminal on the battery.
This method allows engineers to use the whole chassis, engine, and body as a return circuit - assuming the car has a metal body. This also minimizes wire requirements and weight. Plastic body cars need wires from components to a good ground. But they are usually bundled to a common ground to minimize wire usage and weight.