plane wave
A wave whose wavefronts are infinite parallel planes; a fundamental concept in physics and engineering.
Electromagnetic waves are often approximated as plane waves.
The wavefront of a plane wave is a plane perpendicular to the direction of propagation.
orthogonalized plane wave; OPW
Compound of 平面 (plane, flat surface) and 波 (wave). The term is a direct calque from English 'plane wave'.