Permittivity is a property of a material that measures the opposition it offers against an electric field. It is a measure of the electric polarizability of a dielectric in electromagnetism. More generally, permittivity is a thermodynamic function of state that can depend on the frequency, magnitude, and direction of the applied field. The SI unit for permittivity is farad per meter (F/m) . Permittivity is often represented by the relative permittivity εr, which is the ratio of the absolute permittivity ε and the vacuum permittivity ε0. This dimensionless quantity is also often referred to as the permittivity. Another common term encountered for both absolute and relative permittivity is the dielectric constant, which has been deprecated in physics and engineering as well as in chemistry.

Permittivity is a property of every material or medium, which measures the opposition offered against the formation of an electric field. It tells the number of charges required to generate one unit of electric flux in the given medium. The permittivity of an insulating or dielectric material is symbolized as ε. In electrical engineering applications, permittivity is often expressed in relative rather than absolute terms. The higher the value of the dielectric constant, the greater the opposition the material offers against the formation of an electric field.

Permittivity is connected to electric flux (and by extension electric field) through Gausss law. Gausss law states that for a closed Gaussian surface, the net electric flux passing through the surface is equal to the charge enclosed.

In summary, permittivity is a measure of the electric polarizability of a dielectric and is a property of every material or medium that measures the opposition it offers against the formation of an electric field. It is often represented by the relative permittivity εr, which is the ratio of the absolute permittivity ε and the vacuum permittivity ε0. The SI unit for permittivity is farad per meter (F/m).