“Doppler broadening” refers to the broadening of spectral lines in atomic or molecular spectra caused by the Doppler effect. When atoms or molecules move, their emitted or absorbed electromagnetic radiation, typically in the form of spectral lines, appears shifted due to their motion relative to an observer. Doppler broadening occurs because atoms or molecules in a gas or a material have varying velocities and, consequently, different Doppler shifts. This effect results in a broadening of the spectral lines, making them wider and less distinct. Doppler broadening is observed in various fields, including astronomy, where it helps determine the velocities of celestial objects, and in spectroscopy, aiding in the analysis of atomic or molecular structure and dynamics within materials.