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.