In probability theory, a log-normal distribution is a probability distribution of a random variable whose logarithm is normally distributed. If X is a random variable with a normal distribution, then Y = exp(X) has a log-normal distribution; likewise, if Y is log-normally distributed, then X = log(Y) is normally distributed. (This is true regardless of the base of the logarithmic function: if loga(Y) is normally distributed, then so is logb(Y), for any two positive numbers a, b ≠ 1.)
Log-normal is also written log normal or lognormal. It is occasionally referred to as the Galton distribution or Galton's distribution, after Francis Galton.
对数正态分布(lognormal distribution)是当随机变量的对数是正规地分布的时候产生的分布类型。对数正态分布(lognormal distribution)起因于变量是大量的相互独立，恒等分布(identically-distributed)的变量的积。
from:
http://en.wikipedia.org/wiki/Log-normal_distribution