M42 definitions

(astronomy) The Orion Nebula; a diffuse nebula located at a distance of approximately 1600 light years from Earth, in the direction of the constellation Orion.

Origin of m42

From Charles Messier, who first published Nebulae and Star Clusters in 1774 as a listing of visible objects in the night sky that were not stars. Objects in Messier's catalog are numbered, and the letter M (for Messier) is prepended to these numbers.