Student's t-distribution
If we take a sample of n observations from a normal distribution, then the t-distribution with ν = n−1 degrees of freedom can be defined as the distribution of the location of the sample mean , relative to the true mean , divided by the sample standard deviation  over the normalizing term  (that is, ). In this way, the t-distribution can be used to estimate how likely it is that the true mean lies in any given range.