The energy stored in a capacitor is electrostatic potential energy and is thus related to the charge Q and voltage V between the capacitor plates. A charged capacitor stores energy in the electrical field between its plates.

Capacitance: the ability of a system to store an electric charge. The ratio of the change in an electric charge in a system to the corresponding change in its electric potential.

Capacitor: a device used to store an electric charge, consisting of one or more pairs of conductors separated by an insulator.

Coulomb: the SI unit of electric charge, equal to the quantity of electricity conveyed in one second by a current of one ampere.  The coulomb (symbol: C) is the International System of Units (SI) unit of electric charge. Under the 2019 redefinition of the SI base units, which took effect on 20 May 2019, the coulomb is exactly 1/(1.602176634×10 ) elementary charges. The same number of electrons has the same magnitude but opposite sign of charge, that is, a charge of −1 C. 

Farad: the SI unit of electrical capacitance, equal to the capacitance of a capacitor in which one coulomb of charge causes a potential difference of one volt.