regression, In statistics, a process for determining a line or curve that best represents the general trend of a data set. Linear regression results in a line of best fit, for which the sum of the squares of the vertical distances between the proposed line and the points of the data set are minimized (see least squares method). Other types of regression may be based on higher-degree polynomial functions or exponential functions. A quadratic regression, for example, uses a quadratic function (second-degree polynomial function) to produce a parabola of best fit.