Consider charge of consistent surface density (charge-per-area) everywhere on an infinite horizontal plane. In computing the electric field due to such a charge distribution one can use a Gaussian surface in the shape of a tin can whose top is above and parallel to the plane in question and whose bottom is below and parallel to the plane.
How can one notify that the electric flux through the walls of the can is zero? If you eradicate the top of a can and the bottom of the can that which is left a piece that looks like a short length of pipe is what we are calling the walls of the can.