Definition. The total trading volume (in USD) of perpetual (non-expiring) futures contracts where sellers were the aggressors, summed over a rolling 24-hour window.

Technical. Only trades quoted against USD-related currencies (fiat and stablecoins) on the native asset are included. The chosen data resolution (e.g. 10-minute, hourly) determines the cadence at which the trailing 24-hour sum is reported.

Interpretation. Surfaces aggregate sell-side flow on perpetual contracts over the trailing 24 hours, reading as a measure of selling pressure and market sentiment. Answers questions of the form: how much selling activity has there been for BTC perpetual futures in the last 24 hours?