redshift Definition

redshift
noun

1. astron.
An increase in the wavelength of light or other electromagnetic radiation emitted by certain galaxies or quasars.

Etymology: 1920s: so called because an increase in wavelength moves light towards the red end of the visible spectrum, which is generally interpreted as a Doppler effect resulting from the movement of the source of radiation away from the Earth, and is regarded as evidence that the Universe is expanding.