This document discusses t-digest, which provides a compact way to represent a distribution of values. T-digest uses adaptive bins that are smaller near the edges, allowing it to accurately track quantiles even with a limited number of bins. It works by taking data samples, sorting them, and grouping them into bins while respecting a maximum size. The bins can then be merged across samples or time periods. T-digest is useful for applications that need to track distributions over many variables or time periods with limited space.