The Ryan-Joiner statistic measures how well the data follow a normal distribution by calculating the correlation between your data and the normal scores of your data. If the correlation coefficient is near 1, the population is likely to be normal. This test is similar to the Shapiro-Wilk normality test.
Minitab uses the Ryan-Joiner statistic to calculate the p-value. The p-value is the probability of obtaining a test statistic (such as the Ryan-Joiner statistic) that is at least as extreme as the value that is calculated from the sample, when the data are normal. Larger values for the Ryan-Joiner statistic indicate that the data do not follow the normal distribution.