P-Value
Etymology
The “p” stands for probability. The measure was formalized by Ronald Fisher in the 1920s as an informal index of evidence against a null hypothesis; the now-ubiquitous 0.05 threshold was a convenience Fisher himself treated loosely.
noun · /PEE VAL-yoo/
The probability of seeing a result at least as extreme as the observed one, if there were really no effect.
What it names
It is the most cited and most misunderstood number in science, and knowing what it does NOT mean is the whole lesson.
Example
A p-value of 0.04 does not mean there is a 96 percent chance the effect is real — it only means data this striking would be uncommon if nothing were going on.
Related idea
The p-value is not the probability the hypothesis is true, and clearing 0.05 is not proof; chasing low p-values across many tests (“p-hacking”) manufactures statistical significance out of noise.