Question

what does fail to reject the null hypothesis mean?

Answer 1

If our statistical analysis shows that the significance level is below the cut-off value we have set (e.g., either 0.05 or 0.01), we reject the null hypothesis and accept the alternative hypothesis. Alternatively, if the significance level is above the cut-off value, we fail to reject the null hypothesis and cannot accept the alternative hypothesis. You should note that you cannot accept the null hypothesis, but only find evidence against it.

if we fail to reject the null hypothesis, it does not mean the null hypothesis is true. That's because a hypothesis test does not determine which hypothesis is true, or even which is most likely:

it only assesses whether available evidence exists to reject the null hypothesis.