Sentence:  <WSD>Quadratic forms</WSD> of normal random vectors are of great importance in many branches of statistics, such as least-squares methods, the analysis of variance, regression analysis, and experimental design. 
Meaning of the word marked with <WSD> tags:  A scalar quantity of the form \varepsilon^T\Lambda\varepsilon, where \varepsilon is a vector of "n" random variables, and \Lambda is an "n"-dimensional symmetric matrix.