Fundamentally, linear regression seeks to fit a set of data sample by determining the hyperplane (affine) that minimises the mean squared error (MSE) between the data points and the plane. In statistics we seek to find this particular parametric regression \( r(X=x) = E(Y|X = x) \), and if \( Y|X \) follows normal distribution, it can be shown that the minimum MSE is indeed the maximum likelihood estimator (MLE) of the regression.