Simple Definition:

Alternating current (AC) is a type of electrical current that periodically changes direction [flows back and forth]. Unlike direct current (DC), which flows only in one direction, AC continuously switches its flow direction at a certain frequency. This change in direction allows the current to be easily transmitted over long distances using transformers. AC is the most common type of electrical current used in homes and businesses.

Example:
The electricity that powers our lights and appliances at home is alternating current.

Very Simple Definition:

Alternating current (AC) is a type of electricity that goes back and forth [changes direction continuously]. It is the kind of electricity we use in our homes and offices.

Example:
The electricity that makes our lights turn on and our TVs work is alternating current.