A dielectric is a nonconductor of electric charge in which an applied electric field causes a displacement of charge but not a flow of charge. Electrons within the atoms of a dielectric are, on average, displaced by an applied field with respect to the nucleus, giving rise to a dipole that has an electric moment in the direction of the field. The resulting stress within the dielectric is known as the electric polarization (P) and is defined by P = D – E ε₀, where D is the displacement, E is the electric field strength, and ε₀ is the dielectric constant.

The dielectric constant is known called the relative permittivity. The dielectric strength is the maximum potential gradient that can be applied to a material without causing it to break down. It is usually expressed in volts per millimeter.