What is Order Flow?
Aggressors, bid vs ask, and why executed orders lead price.
Order flow is the study of the actual buy and sell orders being executed in real time — who is being aggressive, at what price, and in what size — rather than the shape a candle leaves behind.
Every trade needs two parties: someone resting a limit order (passive liquidity, sitting on the bid or the ask) and someone crossing the spread with a market order to hit it (the aggressor). Order flow classifies each trade by who was aggressive: a trade at the ask is buyer-initiated, a trade at the bid is seller-initiated.
That distinction is the whole point. Traditional volume tells you how much traded; order flow tells you the intent behind it. Because aggression is what actually moves price, reading it well can put you a step ahead of lagging, price-derived indicators.
The core building blocks
- Bid / Ask: the best resting buy and sell prices.
- Aggressor: the market order that consumes liquidity and prints the trade.
- Footprint: the buy vs sell volume at each price inside a candle.
- Delta: aggressive buys minus aggressive sells.
- DOM & Tape: the live order book and the running list of prints.