Why A radio wave carries both an electric field and a magnetic field, at right angles to each other and to the direction of travel. By convention, polarization is named for the orientation of the electric (E) field: if that field is vertical relative to the Earth, the wave is vertically polarized, and a vertical antenna radiates and receives it best. Matching polarization matters because a cross-polarized antenna can lose 20 dB or more of signal on line-of-sight VHF/UHF paths.
Watch out The magnetic field is a real part of the wave and is always perpendicular to the electric field, so it does tell you the orientation indirectly, but the standard definition of polarization references the electric field only.
Polarization = Electric field. Both start with the same idea: E for E-field, and E comes first.