Here is the quote from my NEC Handbook.
"It is imperative that Code users be familiar with the definitions in Article 100, especially those terms associated with this article (250). Specific words to to be aware of are the "grounded conductor", "equipment grounding conductor," and "grounding electrode conductor."
Grounding can be divided into two areas: system grounding and equipment grounding. They are kept separate from each other except at the point where they receive their source of power, such as at the service equipment or a separately derived system.
Grounding is the intentional connection of a current carrying conductor to ground or something that serves the place of ground. In most instances, this connection is made at the supply source, such as a transformer, and at the main service disconnecting means of the premises utilizing the energy.
There are three basic reasons for grounding:
1. To limit the voltages caused by lightning or by accidental contact of the supply conductors with conductors of higher voltage.
2. To stabilize the voltage under normal operating conditions. This maintains the voltage at one level relative to ground, so that any equipment connected to the system will be subject only to that potential difference.
3. To facilitate the operation of overcurrent devices, such as fuses, circuit breakers, or relays, under ground fault conditions."