Full width at half maximum

In telecommunication, a full width at half maximum (FWHM) is an expression of the extent of a function, given by the difference between the two extreme values of the independent variable at which the dependent variable is equal to half of its maximum value.

Note 1: FWHM is applied to such phenomena as the duration of pulse waveforms and the spectral width of sources used for optical communications.

Note 2: The term full duration at half maximum (FDHM) is preferred when the independent variable is time.

Source: from Federal Standard 1037C