Critical region in Machine Learning

A region (corresponding to a statistic t) is called the sample space. The part of the sample space that amounts to a rejection of null hypothesis H0 is called critical region or region of rejection.

Id X = ( x1,x2,x3,.........,xn) is the random vector observed and Wc is the critical region ( prescribed test procedure) of the sample space W, then

                                                                                                       Wa = W - Wc

of the sample, space is called the acceptance region.