Binomial distribution is closely related to normal distribution. Binomial distribution describes the probability distribution of success times in a series of independent repeated experiments, in which there are only two possibilities for the result of each experiment, usually success and failure. Normal distribution is a continuous probability distribution, which is widely used in many natural and social phenomena.

When the number of experiments n of binomial distribution is large enough and the success probability p is close to 0.5, binomial distribution can be approximately described by normal distribution. This is due to the central limit theorem, that is, the sum of a large number of independent random variables approximately obeys normal distribution.