The household outlet in the USA has three the upper two are hot and neutral whereas the third one represents the ground. All these go to the breaker control panel. The positive (hot) and negative (neutral) lines both go to the transmission line, whereas the ground wire connects to a ground rod. Actually, the ground provides a lower resistance path to the fault current. Electrical equipment such as ovens, pc, and others having metals case has their external bodies connected to the ground wire. Doing so provides the protection against the faults thus protecting us from the dangerous menacing current
The most common type of ground in basic electrical circuits is a three or four identical lines one smaller than other an so on. This ground is actually a common reference point which means all points having this symbol will have the same reference voltage.
Chassis ground is another term which represents a continuous piece of metal to whom all other parts of metal are joined/connected. The negative terminal of the battery is also connected to this chassis.
In this video, all the above-explained terms are explained in very simple and easy manner. Watch this Electrical Engineering video and boost your practical Electrical knowledge.