1. Alternating current (AC), is an electric current which periodically reverses direction, whereas direct current (DC) flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions and electric lamps into a wall socket. The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.
2. Alternating Current (AC) is a type of electrical current, in which the direction of the flow of electrons switches back and forth at regular intervals or cycles. Current flowing in power lines and normal household electricity that comes from a wall outlet is alternating current. The standard current used in Europe and most other parts of the world it is 50 cycles per second (i.e. a frequency of 50 Hz.).
https://en.wikipedia.org/wiki/Direct_current (1.); http://www.greenfacts.org/glossary/abc/alternating-current.htm (2.)