The dielectric constant is a measure of a substances ability to insulate charges from each other. It is a measure of the bulk polarity of a solvent, and the higher the dielectric constant of a solvent, the more polar it is. The dielectric constant is also known as relative permittivity, and it is the ratio of a materials permittivity to the permittivity of free space. The dielectric constant represents the ratio of the capacitance of a capacitor whose test material is the dielectric to the capacitance of a capacitor whose dielectric is vacuum (or air) .

The dielectric constant is important in chemistry because it affects solubility. A solvents dielectric constant can help predict how well a solute molecule will dissolve in it. As a general rule, if the dielectric constant of a solvent is high, it is more likely to dissolve polar/ionic compounds. If the dielectric constant is low, the solvent is more suited for dissolving non-polar (non-ionic) compounds.

In summary, the dielectric constant is a measure of a substances ability to insulate charges from each other, and it is a measure of the bulk polarity of a solvent. It is also known as relative permittivity, and it affects solubility in chemistry.