Order statistics refer to the values obtained by arranging a sample of data in ascending or descending order. The k-th order statistic is the k-th smallest value in this ordered list. For example, in a dataset of 5, 2, 9, 1, 7, the second order statistic is 2 after sorting the data to 1, 2, 5, 7, 9. These statistics are useful in various fields, including statistics, data analysis, and machine learning. They help summarize data distributions, identify outliers, and make decisions based on ranked values. Common applications include median and quartiles, which are specific order statistics.