O que é Hypothesis test, null hypothesis, p-value?

A hypothesis test is a rule that, from data $X$, decides whether to reject a null hypothesis $H_0$ (a statement about the law of $X$, such as “the strategy’s mean return is zero”) in favour of an alternative $H_1$. It rejects when a statistic $T(X)$ exceeds a critical value. The $p$-value of an observed $t$ is $\P_{H_0}(T \ge t)$: the probability, under the null, of a statistic at least as extreme as the one seen.