DefinitionLeast square approximation is a method for finding the curve that minimizes the sum of the squares of the differences between observed values and values predicted by the model. Usage : Data Fitting, Regression Analysis, Statistical Modelling. For example, in linear regression, the least squares method finds the line \(y=mx+b\) which minimizes \(\sum(y_i - (mx_i+b))^2\) over all data points \((x_i,y_i)\).