chi-square (chi2) distribution

chi-square (χ2) dis·tri·bu·tion

(kīskwār dis-tri-byūshŭn)
Variable is said to have a chi-square distribution with K degrees of freedom if it is distributed like the sum of the squares of K independent random variables, each of which has a normal (gaussian) distribution with mean zero and variance one. The chi-square distribution is the basis for many variations of the chi-square(d) test, perhaps the most widely used test for statistical significance in biology and medicine.