Student's t Distribution
A probability distribution which is very similar in shape to the standard normal distribution. The mean of the t distribution is always equal to 0, while the standard deviation is usually slightly greater than 1. Only one parameter, called the degrees of freedom, is necessary to completely specify the distribution.
Values of Student's t are frequently used in forming confidence intervals for the mean when the variance is unknown, testing if two sample means are significantly different, or when testing the significance of coefficients in a regression model.
See also: Standard Normal Distribution.