A very large volume number that prints at the high or low of a bar, signalling institutional activity at the extreme. At a bar's high, 2,500 contracts on the ask when normal single-level volume is 200–400 means aggressive retail buyers were lifting offers — and a passive institutional seller was absorbing them, distributing supply at a price they consider advantageous (a "cap" signal). The ratio R_extreme = V_extreme / V_adjacent gg 1 confirms the print; the implication is reversal, because institutions would not let so much paper trade at the high if they expected higher prices.