power function
/ˈpaʊə ˌfʌŋ(k)ʃn/noun
1 Mathematics. A function which relates one quantity to an exponential power of another quantity; a function of the form y = ax n.
2 Statistics. The power of a statistical test as a function of the difference between the means of two sample populations tested.
Origin
Early 20th century. From power + function.