Merriam-Webster Collegiate Dictionary - normal distribution

 noun  Date: 1897 a probability density function that approximates the distribution of many random variables (as the proportion of outcomes of a particular sort in a large number of independent repetitions of an experiment in which the probabilities remain constant from trial to trial) and that has the form f(x) = (1/(?v2?))e(- 1/2(x - ?)/??) where ? is the mean and ? is the standard deviation — compare normal curve