A very small volume number (often 1–9 contracts) at the very high or low of a bar, signalling exhaustion at the extreme. The market probed the level but almost nobody was willing to transact — the last buyer has bought (at a high) or the last seller has sold (at a low). The exhaustion is quantified by the ratio R_extreme = V_extreme / V_adjacent: when adjacent volume dwarfs extreme volume (e.g., 30:1), reversal is likely.