Methodology
The documented rules a provider uses to define and calculate a metric, including what is counted and what is left out.
A methodology specifies which venues and assets are included, how prices from several venues are combined, how supply is estimated, how double counting is handled, how suspected wash trading and outliers are filtered, and what happens when data is missing. It exists because a metric name alone carries almost no information: two figures both labeled total value locked or circulating supply are comparable only if the rules behind them match. Methodologies change over time, and a responsible provider versions them and publishes notes when a definition moves. For research, the citable unit is the metric, the provider, the methodology version, and the date retrieved.
In practice
A provider that begins excluding a category of deposits from its value-locked calculation will show a step change across the whole history, caused by the rule rather than by any withdrawal.
The common misunderstanding
A change in a chart is not always a change in the world; a definition change can move an entire history overnight.