Order flow has its own vocabulary, and a lot of it is jargon nobody stops to define. This glossary collects the terms you will run into over and over when you read the flow, each one explained in a few sentences and linked to its full guide when you want to go deeper. Use it as a quick reference: hit a word you can’t place, look it up here. For the overall framework, always start from the order flow trading guide.
A
Absorption
When a passive trader with large limit orders soaks up all the aggression thrown at a price without letting it move. Thousands of contracts hit a level and price refuses to budge. It is one of the most profitable reads in the flow and often turns the market at support and resistance. More in absorption trading.
Aggressor
Whoever executes against the resting orders in the book using a market order. Aggressors consume liquidity and move price. Their opposite is the passive side, which provides liquidity with limit orders. Telling aggressor from passive is the foundation of all order flow: it is developed in aggressive vs passive orders.
Ask
The best available sell offer, the lowest price anyone is currently willing to sell at. When aggressive buying hits the ask, it prints as a market buy. Volume executed at the ask is the raw material of cumulative delta and the footprint.
Auction
The framework that treats the market as a continuous auction, ticking up until it runs out of buyers and down until it runs out of sellers. It is the conceptual base of balance and imbalance. See auction market theory.
B
Balance
A market state where price rotates inside a range, with buyers and sellers accepting those prices as fair. The volume profile draws a symmetric bell. Its opposite is imbalance. How to tell them apart and trade each is in market balance and imbalance.
Bid
The best available buy offer, the highest price anyone is currently willing to pay. When aggressive selling hits the bid, it prints as a market sell. Volume at the bid is the other half of the delta calculation.
Bid/ask spread
The gap between the best bid and the best ask. In liquid markets like the ES it is one tick; in thin markets it widens. The spread is the implicit cost of crossing the market with an aggressive order. Detailed in bid ask spread.
Big prints
Unusually large trades that show up on the tape or footprint. They signal the presence of size and often mark levels where someone significant took a position. See big prints on the footprint.
C
CVD (cumulative delta)
Cumulative Volume Delta: the running sum of delta across the session. Where delta measures the pressure of a single bar, CVD measures net accumulated pressure. Its divergences with price are exhaustion signals. Explained in the cumulative delta guide.
D
Delta
The result of subtracting volume executed at the bid from volume executed at the ask. A delta of +1,500 means 1,500 more contracts of aggressive buying than aggressive selling. It sums up in one number who won the aggression battle. Everything in cumulative delta.
Delta divergence
A mismatch between delta and price: delta pushes one way but price does not follow. It signals that aggression is failing to get its result, often the prelude to a turn. Detailed in delta divergence.
DOM (depth of market)
The window showing the limit orders stacked at each price above and below the current market. It reveals where passive liquidity is waiting. Guide in depth of market DOM.
F
Footprint
The chart that breaks each candle into price levels and shows, at every one, the volume executed at the bid and the ask. It is order flow made visible and the central tool for most flow traders. Everything in footprint chart.
H
HFT (high-frequency trading)
Fully automated trading that operates at microsecond speeds, providing liquidity and arbitraging tiny edges. It adds a lot of small, fast prints to the tape that flow traders learn to read around. See high-frequency trading and order flow.
HVN / LVN
High Volume Node and Low Volume Node: the high- and low-volume nodes of the profile. HVNs are prices where a lot traded (price magnets); LVNs are thin prices that price tends to cross quickly. See HVN LVN volume nodes.
I
Iceberg
A large order shown to the market in small pieces to hide its true size. Each time the visible slice fills, another appears. It betrays institutional presence. Explained in iceberg orders.
Imbalance (footprint)
An aggression imbalance on the diagonal of the footprint, typically when one side’s volume exceeds the other by a ratio of 300% or more. It pushes price in its direction, and when several stack in a row they mark levels. Guide in order flow imbalances, and the stacked case in stacked imbalances.
Initial balance
The price range of the first hour of the regular session. It serves as a reference for the day: price staying inside leans toward balance, a decisive break leans toward imbalance. See initial balance trading.
Open interest
The total number of open futures contracts that have not yet been closed or expired. Cross-referenced with price, it shows whether a move is driven by new money or just position closing. Everything in open interest in futures.
Opening / closing auction
The concentrated auctions where the most volume of the day is matched at a single price. The open sets the day’s reference; the close is where passive institutional money settles. See opening and closing auctions.
L
Liquidity
The amount of orders available to trade without moving price sharply. A liquid market absorbs large orders with little slippage; a thin one jumps on small volume. Liquidity is what makes the flow reliable. Guide in liquidity in trading.
Limit order
An order you leave at a specific price, waiting for someone to execute against it. It provides liquidity and makes you the passive player. Its opposite is the market order. Compared in order types in trading.
M
Market order
An order that executes immediately against the ones already resting in the book. It consumes liquidity and makes you the aggressor. It is the order that moves price. See order types in trading.
Market microstructure
The study of how prices form at the order level: the book, the priority queue, how trades cross. It is the theory underneath order flow. Explained in market microstructure.
O
Order flow
The real-time record of the orders being executed: how many contracts, at what price, and who was the aggressor. It is the discipline that encompasses footprint, delta, volume profile and tape. The starting point is the order flow trading guide.
P
Passive
Whoever waits with limit orders for someone else to execute against them. Passive traders provide liquidity and do not move price; in absorption, they win. It is the opposite of the aggressor. See aggressive vs passive orders.
POC (point of control)
The price with the most traded volume in a profile. It works as a magnet and a reference: the market tends to return to it. Detailed in point of control POC.
Volume profile
A representation showing how much volume traded at each price, regardless of time. From it come the POC, the value area, and the HVN/LVN nodes. Full guide in volume profile.
S
Speed of tape
The pace at which prints appear on the tape. A fast tape signals urgency and a slow one disinterest; an extreme acceleration at an extreme marks a climax. See speed of the tape.
Spoofing
Manipulation that consists of placing large fake orders to mislead others about real supply or demand, then pulling them before they execute. It is illegal in regulated markets. Explained in spoofing and market manipulation.
Stop hunting
Moves that push price to where clusters of stop-loss orders sit, triggering them to generate liquidity, before reversing. It looks like manipulation but is often just the market seeking liquidity. See stop hunting.
T
Tape (time and sales)
The raw list of every transaction as it happens: price, size, and aggressor. Reading the tape is the most hands-on skill in the flow and reveals nuances an aggregated chart smooths over. Full guide in tape reading.
Tick
The minimum increment a contract’s price moves in. On the ES it is 0.25 points, worth $12.50. Each footprint cell is one tick, and its dollar value defines your risk. Everything in tick size and tick value.
Trapped traders
Traders who entered on the wrong side and are stuck at a loss when price turns against them. Their forced exit (longs selling, shorts buying back) fuels the move against them. See trapped traders.
V
Value area
The range of prices where roughly 70% of a session’s volume traded, with its edges VAH (high) and VAL (low). It marks the market’s zone of acceptance. Guide in value area trading.
Volume analysis
The reading of traded volume as a signal of participation and conviction behind a move. It is the classic bar-volume approach that order flow refines with side-by-side aggression data. See volume analysis in trading.
VWAP
Volume Weighted Average Price: the volume-weighted average price of the session. It is the “fair price” reference many institutions watch. Everything in VWAP trading.
Frequently Asked Questions
Where do I start if I’m new to order flow?
With the base order flow trading guide, which explains the overall framework and links out to the rest. After that, get solid on the fundamentals (aggressor vs passive, bid, ask, the tick) before jumping to the footprint and delta.
What are the four most important terms?
Footprint, delta, volume profile and the tape. Those are the four tools of order flow. If you understand those four and the aggressor-versus-passive distinction, you have the base to read flow.
What’s the difference between delta and volume?
Volume counts how many contracts traded; delta counts the difference between aggressive buying and selling within that volume. The same volume can carry a very positive, negative or neutral delta depending on who dominated the aggression.
Do these terms work the same in crypto and futures?
The vocabulary is identical in any centralized, liquid market: futures like the ES or NQ and the major crypto perpetuals. What changes is the reliability of the data depending on the instrument’s liquidity, not the meaning of the terms.