means A device that produces a narrow, intense beam of light in which all the waves are aligned and the same color, used for everything from surgery to barcode scanners to cutting steel.

from Not a word handed down but one built to order: an acronym for 'Light Amplification by Stimulated Emission of Radiation,' coined in 1959 by physicist Gordon Gould. It rides on the coattails of an earlier sibling, the maser (the same trick done with microwaves), and the underlying idea of 'stimulated emission' traces back to Einstein in 1917. So 'laser' is a word that started life as a sentence — its whole engineering spec folded into five tidy letters.