The Mann-Whitney U test is a non-parametric statistical test used to compare differences between two independent groups. It assesses whether one group tends to have higher or lower values than the other, without assuming a normal distribution of the data. This makes it useful for analyzing ordinal data or when sample sizes are small. To perform the test, the data from both groups are ranked together, and the U statistic is calculated based on the ranks. The resulting U value helps determine if there is a statistically significant difference between the two groups, providing insights into their relative distributions.