In mass spectrometry, mass resolution is basically how sharp your spectral peaks are. Unlike in structural biology, higher numbers correspond to higher resolution (sharper peaks). Mass resolution is often calculated using the formula: (m/z)/FWHM == (m/z)/(w1/2) == (m/z)/half-height

FWHM, aka w1/2, or is “half-height” is Full Width-Half Maximum height. It’s 1/2 the width at the base of a peak. The sharper the peak, the smaller the FWMH, and thus the higher the resolution.