"Laser" is an acronym for "Light Amplification by Stimulated Emission of Radiation", coined by the laser pioneer Gordon Gould. Although this original meaning denotes an operation principle, the term is nowadays mostly used for devices generating light based on the laser principle.

In physics, a laser is a device that emits light through a specific mechanism for which the term laser is an acronym: light amplification by stimulated emission of radiation. This is a combined quantum-mechanical and thermodynamical process discussed in more detail below. As a light source, a laser can have various properties, depending on the purpose for which it is designed. A typical laser emits light in a narrow and well-defined beam and with a well-defined wavelength (or color).