When testing hypothesis there might be a situation where we reject but also won't accept the alternative hypothesis because the statistic calculated from the sample fell into a region that separates the hypothesis.

When is true, but we retain , then we are making a Type II error.

When the statistic, that is calculated from our sample, falls into the critical region, then we retain .

When testing hypothesis we retain , there is still a possibility that actually is true, but we are not able to show this with the given data;