DFB laser linewidth is the most important specs and features for the DFB lasers. The DFB laser linewidths may be MHz or KHz . Such as this 1290nm DFB Laser, it has linewidth of 3MHz ; 1330nm DFB laser with linewidth of 3MHz .

DFB Laser Linewidth is the Laser Linewidth of the DFB Lasers. DFB laser is one type of semiconductor lasers.  DFB lasers use the Bragg reflection of a diffraction grating formed along an active waveguide to unify the laser longitudinal mode. DFB provides high wavelength stability and narrow linewidth.

Laser linewidth or Laser spectral linewidth,

Laser linewidth is the spectral linewidth of a laser beam. Two of the most distinctive characteristics of laser emission are spatial coherence and spectral coherence. While spatial coherence is related to the beam divergence of the laser, spectral coherence is evaluated by measuring the linewidth of laser radiation.

Check this article about Laser spectral linewidth.