In probability and statistics, Student's t-distribution (or simply the t-distribution) is any member of a family of coutinuous probability distributions that aries when estimating the mean of a normally distributed population in situations where the sample size is small and population standard deviation is unknown.

In the t-distribution, ν the degrees of freedom as n - 1 (n observations from a normal distribution)

In probability theory, the normal (or Gaussian) distribution is a very common continuous probability distribution. the cental limit theorem.

In probability theory and statistics, the logistic distribution is a continuous probability distribution. Its cumulative distribution function is the logistic function. It resembles the normal distribution in shape but has heavier tails (higher kurtosis).

All stuff here are from wikipedia.