Sentence:  The analysis of diffraction-line broadening is one of the most powerful methods to quantitatively analyze defects in crystalline materials. Values for crystallite-size and <WSD>microstrain</WSD> parameters can be obtained according to a variety of methods. 
Meaning of the word marked with <WSD> tags:  The root mean square of the variations in the lattice parameters across the individual crystallites, usually across microscopic distances, <ϵ2>1/2. By definition, it cannot be negative. In contrast, macrostrain refers to the overall change in the lattice parameters caused by a composition change or temperature change or pressure change.