There is a source of current from which the flow of current in the circuit changes direction spontaneously at a regular interval. This current is called alternating current (Figure).
Alternating current describes the flow of charge that changes direction periodically. As a result, the voltage level also reverses along with the current. AC is used to deliver power to houses, office buildings, etc. In abbreviated form, it is written as A. C. That means the flow of current that changes direction or phase at regular interval of time is called alternating current. This current, while flowing in a particular direction, gradually increases and readies a maximum value and then gradually decreases and becomes zero while changing direction.
This comes from power plants that are controlled by the electric company. Those big wires you see stretching transversely the countryside are carrying AC current from the power plants to the loads, which are in our homes and businesses.