Dielectric constants of a medium

Dielectric constant is defined for medium as the ratio of permittivity of the medium to the permittivity of free space

The dielectric constant is also called the relative permittivity of the medium. Where permittivity is physical significance to permit the charge flow in a medium
Dielectric constant will be different for different materials and also it depends upon the temperature and pressure. Dielectric constant for the same material will be different for AC current and DC current. Dielectric constant varies according to the frequency in case of AC current.