Elliptical polarization: In electromagnetic wave propagation, polarization such that the tip of the electric field vector describes an ellipse in any fixed plane intersecting, and normal to, the direction of propagation.
Note 1: An elliptically polarized wave may be resolved into two linearly polarized waves in phase quadrature with their polarization planes at right angles to each other.
Note 2: Circular and linear polarization are special cases of elliptical polarization.
Source: from Federal Standard 1037C and from MIL-STD-188 and from MIL-STD-2196