wavefront
The surface defined by the locus of points that have the same phase, i.e., have the same path length from the source. [After 2196]
Note 1: The wavefront is perpendicular to the ray that represents an electromagnetic wave.
Note 2: The plane in which the electric and magnetic field vectors lie is tangential to the wavefront at every point.
Note 3: The vector that represents the wavefront indicates the direction of propagation.
Note 4: For parallel, i.e., collimated, rays, the wavefront is plane. For rays diverging from a point, or converging toward a point, the wavefront is spherical. For rays with varying divergence or convergence, the wavefront has other shapes, such as ellipsoidal and paraboloidal, depending on the nature of the source.