Broadening due to the random motion of the emitting or absorbing atoms. A Doppler broadened line has a Gaussian shape.
Source:
PAC, 1985, 57, 1453. 'Nomenclature, symbols, units and their usage in spectrochemical analysis - V: Radiation sources (Recommendations 1985)' on page 1463 (https://doi.org/10.1351/pac198557101453)