Percentiles and quantiles are essential statistical concepts used to understand data distribution. A percentile indicates the value below which a certain percentage of observations fall; for instance, the 70th percentile represents the value below which 70% of the data points lie. Quantiles, on the other hand, divide a dataset into equal parts, with quartiles (four parts) and deciles (ten parts) being common examples. Both measures help in summarizing and interpreting data, allowing for better insights into trends and patterns. Understanding these concepts is crucial for data analysis in various fields, including statistics, finance, and machine learning.