What does vertical wave polarization mean?

Just like with horizontal polarization, vertical polarization is defined entirely by the direction of the wave's electric field. When the electric lines of force are perpendicular (straight up and down) relative to the Earth's surface, the wave is vertically polarized. Any answer choice focusing on the magnetic lines of force is a distractor. Because the magnetic field is always perpendicular to the electric field, a vertically polarized wave will actually have its magnetic lines parallel to the Earth's surface, not perpendicular.