p-value

A p-value is, colloquially, a notion of evidence against the null in hypothesis testing. Mathematically, they are typically defined as a random variable $P$ such that, under the null hypothesis $H_0$, obey

$${\mathbb{P}}_{H_0}(P\le \alpha )\le \alpha ,\forall \alpha \in (0,1).$$

See issues with p-values and p-hacking.