- a band of equidistant, parallel lines, usually more than 5000 per inch (2000 per centimeter), ruled on a glass or polished metal surface for diffracting light to produce optical spectra.
- a glass plate or a mirror with a large number of equidistant parallel lines or grooves on its surface. It causes diffraction of transmitted or reflected light, ultraviolet radiation, or X-rays
- A polished surface, often of glass or metal, having many fine parallel stripes or slits through which radiation such as light is passed and projected onto a screen or other detection device. The interference patterns cast by the diffraction grating on the screen or detector can be analyzed to determine the frequency of the radiation. See also interferometer.