It is the bending of radiation (such as light) around the edge of an obstacle or by a narrow aperture. Diffraction results from the interference of light waves that pass an opaque body, producing a fuzzy region between the shadow area and the lighted area that, upon close examination, is actually a series of light and dark lines.

A diffraction grating contains many fine, parallel slits or scratches (about 12,000 per cm to 30,000 per inch) and disperses light into its colours. These gratings are used in diffracting spectoscopes. The atomic and molecular structure of crystals is examined by X-ray diffraction.