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.

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

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

Source: from Federal Standard 1037C