A p-value is the measure of probability that the null hypothesis was rejected when in fact the null hypothesis is true. When thinking about the standard normal distribution (bell curve), the p-value corresponds to the area under the curve where extreme values are not likely to be the result of chance. The p-value can be calculated using a calculator with the test statistic (z-test or t-test).

The p-value is related to the significance level. If the critical alpha value is 0.05, then the p-value must be smaller than 0.05 for the test to have a statistically significant result. If the p-value is greater than the critical alpha value, then the test does not have a statistically significant result.