Order-flow imbalance measures the difference between aggressive buying and aggressive selling — trades that hit the bid (sellers in a hurry) versus lift the offer (buyers in a hurry). It's a real-time read on which side is being more aggressive, derived from the tape and the order book.

How it differs from volume

Plain volume is directionless — it counts every trade equally. Imbalance separates the aggressors: heavy volume with balanced flow is a fair fight, but heavy volume skewed toward buyers lifting offers shows demand overpowering supply. Two bars can have identical volume and opposite imbalance — the imbalance is where the intent lives.

Why it hints at direction

Persistent one-sided aggression tends to move price — if buyers keep lifting offers faster than sellers refill them, price rises. Sustained imbalance is a short-term momentum tell; a sudden flip (aggressive buying that abruptly turns to aggressive selling) can mark a near-term turn. It's one of the most immediate reads available.

Price is the result. Order-flow imbalance is the pressure that produced it — sometimes a step ahead.

The caveats

Imbalance is noisy and easily faked — a large aggressive print can be a hedge, not a directional bet, and spoofing muddies the book. It's most useful confirming a move at a real level and alongside dealer positioning, not as a standalone trigger. Reading aggression is a core input to how a systematic tape-reader gauges the very short term.