Circular polarization: In electromagnetic wave propagation, polarization such that the tip of the electric field vector describes a helix.
Note 1: The magnitude of the electric field vector is constant.
Note 2: The projection of the tip of the electric field vector upon any fixed plane intersecting, and normal to, the direction of propagation, describes a circle.
Note 3: A circularly polarized wave may be resolved into two linearly polarized waves in phase quadrature with their planes of polarization at right angles to each other.
Note 4: Circular polarization may be referred to as "right-hand" or "left-hand," depending on whether the helix describes the thread of a right-hand or left-hand screw, respectively.
Source: from Federal Standard 1037C and from MIL-STD-188