The surplus of buy or sell orders at the close, which moves the last ten minutes of the session. Sometimes mislabeled as the closing order gap; the platform's term is MOC Imbalance.
What this imbalance is
MOC imbalance (MOC Imbalance) is the surplus of "execute at the close" orders on one side over the other, announced by the exchange shortly before the bell. For example, a net $2 billion of buying must find sellers in the last minutes, which creates measurable pressure on the direction of the close.
Where it comes from
From institutional crowds bound to the closing price: index funds benchmark to it, monthly and quarterly rebalances execute at it, and index changes force buying of entrants and selling of leavers at it. Their orders gather in a single window, and the imbalance is born.
How its effect is traded
A large announced buy imbalance tends to push the last minutes higher until supply absorbs it, and the reverse for sells. It stands out on scheduled-event days (major expirations, quarterly rebalances), when imbalances swell to many times the usual and the closing move becomes an event in itself.
Hypothetical example
A quarterly-expiration Friday when the exchange announces a $3B buy imbalance minutes before the bell: the final minutes see a steady climb despite a sluggish day. It is not late optimism but benchmark-tracking orders buying at any available price.
Common mistake
Reading every imbalance as tomorrow's signal: its effect mostly lives and is absorbed in the closing minutes. It is a market-plumbing phenomenon, not a directional view, and stretching its meaning beyond its window asks more of it than it can give.
Where to see it on the platform
The macro and liquidity tools track the closing window and its scheduled events, and the expiration calendar marks the days when the effect swells.
Why it is read in the last hour
Closing orders pile up just before the bell, so the imbalance says which side will press in the last minutes, minutes that concentrate more volume than whole hours. Its value ends when the session ends: a piece of timing information, not a lasting direction.
Where to see it on the platform
The MOC imbalance panel shows the net figure and the time it was measured before the bell.
