Definition. The total trading volume (in USD) of perpetual (non-expiring) futures contracts where sellers were the aggressors, summed within the intraday window set by the chosen data resolution (e.g. 10-minute, hourly).

Technical. Only trades quoted against USD-related currencies (fiat and stablecoins) on the native asset are included.

Interpretation. Surfaces intraday sell-side flow on perpetual contracts, reading as a measure of immediate selling pressure and short-term market sentiment. Answers questions of the form: how much selling activity has there been for BTC perpetual futures in the last hour?