Diffraction is the interference or bending of waves around the corners of
an obstacle or through an aperture into the region of geometrical shadow of
the obstacle/aperture. The diffracting object or aperture effectively becomes
a secondary source of the propagating wave. Italian scientist Francesco Maria
Grimaldi coined the word diffraction and was the first to record accurate
observations of the phenomenon in 1660.
In classical physics, the diffraction phenomenon is described by the
Huygens–Fresnel principle that treats each point in a propagating wavefront as
a collection of individual spherical wavelets.