A Summary metric in Prometheus is used to track individual observations and calculate quantiles over time.It provides count, sum, and optional quantile values for the observations.Summary metrics are useful for tracking response times, latency, GC time, and operation durations.To define a Summary object, you can specify the name, help, and quantile values.Quantile calculations involve sorting observations and determining percentile values.An application example demonstrates creating a Summary metric for query execution duration.The server setup includes endpoints for simulating queries and exposing metrics.Viewing metrics reveals quantile values, count, sum, and average execution time.Quantiles are approximations maintained through sampling algorithms by Prometheus client libraries.Summary metrics help analyze the distribution of observations for better insights into system performance.