1. Electromagnetic radiation, such as radiation from an injection-locked laser operating above the lasing threshold, emitted when the energy level of an internal quantum system, such as electron energy levels in a population of molecules, drops to a lower energy level when induced to do so by the simultaneous presence of radiation of suitable wavelength. 2. In a laser, the emission of photons, i.e., lightwaves, caused by a signal applied to the laser such that the response is directly proportional to, and in phase coherence with, the electromagnetic field of the stimulating signal, this coherency between applied signal and response being the key to the operation and usefulness of the laser. 3. In a quantum mechanical system, radiation emitted when the internal energy of the system drops from an excited level to a lower energy level when induced by the presence of radiant energy at the same frequency. Note: An example of stimulated emission is the radiation from an injection-laser diode operating above the lasing threshold. See also coherenc,  coherent,  electromagnetic field,  electromagnetic radiation,  electron,  emission,  emit,  energy level,  frequency,  injection-laser diode,  injection-locked laser,  laser,  lasing,  lasing threshold,  light amplification by stimulated emission of radiation,  lightwave,  operation,  photon,  quantum,  radiant energy,  radiation,  resonant cavity,  response,  signal,  simultaneous,  spontaneous emission,  system,  wavelength.