line width

https://doi.org/10.1351/goldbook.L03567
Width of a spectral line in terms of wavelength, frequency or wavenumber. Usually defined as full or half width of the line at half of the maximum intensity FWHM or HWHM, respectively).
Source:
Green Book, 2nd ed., p. 31 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)