High Quality Content by WIKIPEDIA articles! In statistics, the Q-function is the tail probability of the standard normal distribution. In other words, Q(x) is the probability that a standard normal random variable will obtain a value larger than x. Other definitions of the Q-function, all of which are simple transformations of the normal cumulative distribution function, are also used occasionally. In mathematics, the error function (also called the Gauss error function) is a special function (non-elementary) of sigmoid shape which occurs in probability, statistics, materials science, and partial differential equations.