A price level at which the auction was left incomplete — the extreme of a bar shows bid volume but zero ask volume at the next tick above (or ask volume at the low but zero bid volume one tick below). The market typically returns within one to three sessions to "complete" the auction at that level. The trading rule is to mark unfinished-business levels and watch the footprint on the revisit for acceptance (price moves through with imbalances) or rejection (price reverses with opposing imbalances).