Short wavelength electromagnetic radiation usually produced by bombarding a metal target in a vacuum. Used to create images of the internal structure of objects; this is possible because X-rays pass through most objects and can expose photographic film.

(transitive, informal) To take a radiograph of; to obtain an image of using X-ray radiation, especially for the purpose of medical diagnostic evaluation.

A sunbeam seen just after sunset or just before sunrise, caused by a cloud below the horizon and dust particles in the air above the horizon. / A cloud shadow cast on the bright sky.

(optics) A ray that passes through the axis of the optical fiber.

(engineering) Electromagnetic waves with frequencies intermediate between, and sharing properties of both, short radio waves and long IR optical waves. This region is defined variously as between 0.1 - 10 THz, 0.3-3 THz or 0.3-30 THz.

(science fiction) A fictional beam of radiation that can kill.

(science fiction) A fictional weapon that emits harmful rays.

Alternative spelling of gamma ray

Very high frequency (and therefore very high energy) electromagnetic radiation emitted as a consequence of radioactivity.

(astronomy) An energetic particle originating outside our solar system. / (astronomy) Cosmic radiation: a stream of cosmic rays.