how is a wavefront related to the direction of corresponding rays?

Wavefronts and Huygen's Principle. A wavefront is a surface over which an optical wave has a constant phase. ... The direction of propagation of the wave is always perpendicular to the surface of the wavefront at each point.

Wave front, imaginary surface representing corresponding points of a wave that vibrate in unison. When identical waves having a common origin travel through a homogeneous medium, the corresponding crests and troughs at any instant are in phase; i.e., they have completed identical fractions of their cyclic motion, and any surface drawn through all the points of the same phase will constitute a wave front