1. An imaginary line in which each segment of the line is parallel to the direction of the electric field or the direction of the electric displacement at that point, and the density of the collection of the line is relative to the electric field or the electrical displacement.
2. The electric lines of force that make up an electric field or region.
3. The integral over a surface of the component of the electric displacement perpendicular to the surface and equal to the number of electric lines of forces crossing the surface.

The electric field intensity multiplied by the permittivity (measure of the ability of a nonconducting material to retain electric energy when placed in an electric field) or the property of a dielectric medium which determines the forces that electric charges placed in the medium exert on each other.