Glossary

Diffraction: divergent nature of a wave due to its limited size
Aperture : diaphragm limiting the number of light rays that are able to propagate
Wavelength ( of a light wave ): distance between two consecutive identical states of the electric ( or magnetic ) field
Divergence: defines the maximum angle between the light rays of a beam
Airy pattern: pattern representing the intensity distribution of a plane monochromatic light wave diffracted by a circular aperture