Glossary

Spectral width: difference between the largest and smallest wavelengths (frequencies) of the spectrum emitted by a light source, transmitted by an optical system or detected by a photodetector, etc.; the largest and smallest wavelengths (frequencies) are often defined at Full Width Half Maximum (FWHM)
Frequency: reverse value of the period
Wavelength ( of a light wave ): distance between two consecutive identical states of the electric ( or magnetic ) field