p-value

The p-value is the probability of seeing data at least as extreme as yours if the null hypothesis were true. A small p-value (say 0.01) means “this data would be surprising in a world with no real effect,” which counts as evidence against the null.

It is the single most misread number in statistics. The p-value is NOT the probability that the null hypothesis is true, NOT the probability your result was a fluke, and NOT a measure of effect size — a tiny, useless effect can earn a tiny p-value in a huge sample. It is a statement about data given a hypothesis, not about the hypothesis given the data.