Define dielectric constant.

(N/A) The dielectric constant $(K)$,also known as the relative permittivity $(\epsilon_r)$,is defined as the ratio of the permittivity of a substance $(\epsilon)$ to the permittivity of free space $(\epsilon_0)$.
Mathematically,it is expressed as: $K = \frac{\epsilon}{\epsilon_0}$.
Alternatively,in the context of a capacitor,it is defined as the ratio of the capacitance of a capacitor with the dielectric medium $(C)$ to the capacitance of the same capacitor with a vacuum $(C_0)$: $K = \frac{C}{C_0}$.