APA Dictionary of Psychology

a theoretical probability distribution that plays a central role in testing hypotheses about population means, among other parameters. It is the sampling distribution of the statistic (M – μ₀)/s, where μ₀ is the mean of the population from which the sample is drawn, M is the estimate of the mean of the population as obtained from sample data, and s is the standard deviation of the data set. Also called Student’s t distribution.