A capacitor is a device that stores electrical energy in an electric field. It is composed of two conductors separated by an insulator, called the dielectric. The conductors are usually metal plates, and the dielectric can be air, paper, ceramic, or plastic. When a voltage is applied to the capacitor, it creates an electric field between the conductors that stores energy.

The amount of energy stored in a capacitor depends on its capacitance, which is measured in farads (F). The capacitance of a capacitor is determined by its size and shape as well as the type of material used for the dielectric. A larger plate area or a thinner dielectric will result in a higher capacitance.

Capacitors are used extensively in electronic circuits because they can store large amounts of energy relatively cheaply and safely compared to other methods such as batteries. They are also usedin power conditioning applications to smooth out fluctuations in voltage from AC power lines before the electricity reaches sensitive electronic equipment.