1. n. [Formation Evaluation]

The degree to which a medium resists the flow of electric charge divided by the degree to which free space resists such charge. The degree, or dielectric permittivity, is defined as the ratio of the electric displacement to the electric field strength. The term is also known as the relative dielectric constant. However, at high frequencies, it is no longer constant and decreases with frequency. Relative dielectric permittivities, which are unitless, vary from about 4 to 400 in rock, but in rare cases may reach several thousand.

See: dielectric propagation log,  dielectric resistivity,  electromagnetic propagation measurement