Answer/Step-by-step explanation:

The t-distribution, also known as the Student's t-distribution, is a probability distribution that is used in hypothesis testing when the sample size is small or the population standard deviation is unknown. It is similar to the normal distribution but has heavier tails, which allows for greater variability in small sample sizes. The t-distribution is characterized by its degrees of freedom, which determines the shape of the distribution.

Normal distribution and +- distribution refer to the same thing, which is a probability distribution that is symmetric and bell-shaped. The difference lies in how the distribution is defined. Normal distribution is defined in terms of the mean and standard deviation of the population, while +- distribution is defined in terms of the mean and a fixed number of standard deviations from the mean. For example, a +- distribution with a mean of 0 and a standard deviation of 1 would include all values between -1 and 1 standard deviations from the mean, which is equivalent to the central 68.27% of a normal distribution.