A Distributed Bragg Reflector laser has diffraction grating on one or both end mirrors, which reflect a narrow band of light back in the cavity which help them be more spectrally stable.
A resonant cavity is defined by a highly reflective DBR mirror on one end, and a low reflectivity cleaved exit facet on the other end. So DBR lasers tend to be more spectrally stable than Fabry-Perot lasers with broadband coatings. These longitudinal diffraction grating mirrors reflect the light back in the cavity, very much like a multi-layer mirror coating. If one or both of these end mirrors are replaced with a diffraction grating, the structure is then known as a DBR laser (Distributed Bragg Reflector). The diffraction grating mirrors tend to reflect a narrower band of wavelengths than normal end mirrors, and this limits the number of standing waves that can be supported by the gain in the cavity. 
