Definition of Capacitor
Capacitors are usually referred to it as capacitance, with the letter C, said.
Definition 1: The capacitor, by definition, is 'power containers loaded', is a device to accommodate the charge. English name: capacitor. Capacitors are electronic devices, one of large-scale use of electronic components widely used in blocking, coupling, bypass, filtering, tuning circuits, energy conversion, control circuit and so on.
Definition 2: capacitor, and the interval between any two close to each other insulated conductors (including lead), are all constitute a capacitor.

The role of the capacitor in the circuit
In the DC circuit, the capacitor is equivalent to open circuit of the.
This begins with talking about the structure of capacitor. The simplest is a capacitor plate and intermediate at both ends of the insulating dielectric [2] posed. Power, the electrically charged plates to form a voltage (electrical potential difference), but the middle of the material because it is insulated, so it is not conductive. However, this situation is that the capacitor does not exceed the critical voltage (breakdown voltage) under the conditions of the premise. We know that any material is relatively insulated, when the voltage across the material to increase to a certain extent, the substance can be conductive, and we call this voltage is called breakdown voltage. Capacitance is no exception, capacitor breakdown, the body of the insulator is not. However, in secondary school, so that the voltage in the circuit is not seen, so are the following work breakdown voltage, and can be read as an insulator.
However, in the AC circuit, because the current time into a certain direction is a function of change. The capacitor charging and discharging process is time, and this time, changes in the electric field formed between plates, and this electric field is also a function of change over time. In fact, the current through the field in the form passed by the capacitor.
In secondary schools, there is a saying, called Link exchange, blocking DC, that is the capacitance of this nature.

The basic functions of the capacitor - the charge and discharge
Capacitor charging and discharging are the basic functions.
Charge
So that charged capacitor (storage charge and energy) is called charging. Then two plate capacitor is always a positively charged plate and another plate with the same amount of negative charge. The capacitor plate then a power supply (eg battery) is positive, then the power supply to another plate negative, two plates were put on the same amount of the heterogeneous charge. After charging the capacitor between the bipolar plates have a electric field, the charging process to obtain electricity from the power stored in the capacitor.
Discharge
To charge capacitor after the loss of charge (the release of charge and energy) is called discharge. For example, using a wire connected to the capacitor poles, two poles with each other and in charge on the capacitor will charge and release energy. After the capacitor discharge electric field between the disappearance of the bipolar plates, electrical energy into other forms of energy.
In general electronic circuits commonly used to achieve the bypass capacitor, coupling, filtering, oscillation, phase shift and waveform transformation and so on, these effects are the charge and discharge of its functions evolution.