Why An antenna radiates an electromagnetic wave with an electric field and a magnetic field at right angles to each other, and by convention polarization is named for the direction of the electric field. For a simple wire or whip antenna the electric field lines up with the conductor, so a vertical whip produces vertical polarization and a horizontal dipole produces horizontal polarization. Matching polarization between stations matters because a cross-polarized pair can lose 20 dB or more of signal.
Watch out The magnetic field is a real part of the wave, but it sits perpendicular to the electric field, so naming it would reverse every polarization label; the element's physical orientation is only a handy clue, not the definition.
Polarization = E for Electric field. Vertical whip, vertical E, vertical polarization.