what is meant by the critical region? the critical or rejection region is the range of test values that indicates that there is a significant difference and that the null hypothesis should be rejected. the critical or rejection region is the range of test values that indicates that there is a significant difference and that the null hypothesis should not be rejected. the critical or rejection region is the range of test values that indicates that there is not a significant difference and that the null hypothesis should not be rejected. the critical or rejection region is the range of test values that indicates that there is not a significant difference and that the null hypothesis should be rejected.