Final answer:
The level of significance of a hypothesis test is best used to define the test's rejection points, which are the values that would lead to rejecting the null hypothesis.
Step-by-step explanation:
The level of significance of a hypothesis test is best used to define the test's rejection points. The level of significance, denoted as alpha (α), is the probability of making a Type I error (rejecting the null hypothesis when it is true). It helps determine the critical region or rejection region, which is the range of values that would lead to rejecting the null hypothesis.