Huygens' Principle: Huygens' principle states that every point on a wavefront can be considered as the source of a secondary spherical wavelet, and the wavefront at a later time is the envelope of these wavelets.
Interference:Interference is the phenomenon where two or more waves superimpose to form a new wave pattern, which can result in constructive or destructive interference depending on the relative phases of the waves.
Diffraction:Diffraction is the bending of waves around the edges of an obstacle or aperture, which can be explained by the propagation of wavefronts.