In probability theory, a log-normal (or lognormal) distribution is a continuous probability distribution of a random variable whose logarithm is normally distributed. Thus, if the random variable $$X$$ is log-normally distributed, then $$Y=\ln(X)$$ has a normal distribution. Equivalently, if $$Y$$ has a normal distribution, then the exponential function of $$Y$$, $$X=\exp(Y)$$, has a log-normal distribution. A random variable which is log-normally distributed takes only positive real values. (Wikipedia)