Electric Flux

Electric flux is amount of electric field that perpendicularly flow through a certain area. The electric flux, usually written as $\phi$, is directly proportional the number of electric field lines that go through a certain area perpendicularly.

$\phi = E\cdot S = E*S*cos(\theta)$

where $E$ is the uniform electric field, $S$ is the area and $\theta$ being the angle of the electric field to the perpendicular.

In the case of a non-linear electric field, then Gauss's Law is used.