Active Trading Glossary
Active Trading Glossary
This glossary covers the essential terms and concepts referenced throughout this book. Whether you are learning the mechanics of order execution or evaluating the probabilistic edge in a trading system, these definitions provide the practical context needed to understand active trading as both a business and a discipline.
Average True Range (ATR)
A volatility indicator that measures the average movement range of an asset over a set period, typically fourteen bars.
ATR captures how much an asset moves on average, regardless of direction. A stock with an ATR of 2.50 on a daily chart typically moves about 2.50 points per day. Traders use ATR to set stop-loss distances, position sizes, and to filter entry signals—a breakout in a low-volatility environment carries different risk than one in a high-volatility market.
Backtesting
The process of testing a trading strategy against historical price data to measure its historical performance.
Backtesting reveals what a strategy would have earned or lost if applied to past market conditions. Running a strategy that buys breakouts above a twenty-day high from 2015 to 2020 reveals its profit factor, drawdown, and win rate over that period. The danger lies in curve fitting—tuning a strategy so heavily to past data that it fails on fresh data.
Bid-Ask Spread
The difference between the price at which a buyer will purchase (bid) and the price at which a seller will sell (ask).
If you see a bid of 49.95 and an ask of 50.05, the spread is 0.10. Tight spreads (tenths of a cent in liquid stocks) mean lower slippage; wide spreads (especially in illiquid assets) eat into every trade. Spreads widen during market chaos and narrow when participation is high.
Block Trade
A large, privately negotiated transaction between institutional buyers and sellers, typically conducted off the public exchange.
A pension fund may negotiate a block of 500,000 shares at a set price with an investment bank to avoid moving the market. Block trades are one signal of institutional interest and can precede significant price moves, though they are not always reported in real time.
Breakout
A price move that breaks above a previous high or below a previous low with conviction, often signaling a new trend or shift in momentum.
A stock that trades sideways between 50 and 52 for three weeks then rallies to 55 on high volume has broken out above resistance. Breakouts are a popular entry signal, though not all breakouts succeed—many fail, producing whipsaws that trap impulsive traders.
Curve Fitting
Optimizing a strategy's parameters so finely to historical data that the strategy loses its edge on new, unseen data.
A trader might adjust a moving average strategy for a specific start date, stock, or timeframe and achieve a 65 percent win rate on past data. When applied to a different stock or period, the same parameters yield 40 percent wins. Curve fitting is the bridge between illusion of edge and the cold reality of live performance.
DAS Trader
A professional trading platform, commonly used by day traders and scalpers, that provides direct market access, Level 2 data, and rapid order execution.
DAS Trader is favored for its speed and customization, allowing traders to route orders through different venues and execute trades in milliseconds. The platform is expensive and complex, targeting retail traders who can afford the subscription and have the discipline to master its tools.
Day Trading
The practice of opening and closing one or more positions on the same trading day, capturing short-term price movements while avoiding overnight risk.
A trader might buy a stock at 10:00 a.m., sell at 11:45 a.m., and end the day flat. Day traders live or die by intraday volatility, tick-by-tick order flow, and the discipline to exit losses before the market closes. Day trading is regulated—traders with <25,000 in account equity are restricted to three day trades per rolling five-day period.
Direct Market Access
Technology that allows a trader to send orders directly to exchanges and market makers, bypassing broker intermediaries.
With DMA, your order reaches the exchange's matching engine in microseconds, improving fill quality on large orders. Without DMA, a broker may route your order through its own systems, introducing latency and the risk that the broker fills you at a worse price than the market.
Drawdown
The peak-to-trough decline in account equity during a period of trading, usually expressed as a percentage.
If your account is worth $100,000, rises to $130,000, then falls to $95,000, the drawdown is from $130,000 to $95,000 (27 percent). Drawdowns test a trader's psychology and capital; an account that falls 50 percent requires a 100 percent gain to return to breakeven.
Edge
A consistent, repeatable advantage in a trading system that produces a positive expectancy over many trades.
If you have an edge, your system wins more than it loses, or wins larger amounts than it loses, on balance. A trader with an edge might win 52 percent of trades but with an average win of 1.5 times the average loss, producing a positive expectancy of +0.25 percent per trade.
Expectancy
The average profit or loss per trade, calculated as (win rate × average win) minus (loss rate × average loss).
A strategy with a 55 percent win rate, average win of $150, and average loss of $100 has an expectancy of 0.55 × 150 − 0.45 × 100 = $82.50 per trade. Expectancy is one of the most honest measures of a trading system's quality.
Fill
The execution of a trade order at a particular price.
You place a market order to buy 100 shares at the current market price; the broker fills you at 50.02 a share. Fills in illiquid assets or during market chaos may be worse than expected; fills in liquid stocks are often at or near your requested price.
Forward Testing
Testing a trading strategy on new, live market data that the strategy was not optimized for, to validate its edge in real conditions.
After backtesting a strategy on 2020–2022 data, you paper trade it on 2023–2024 data without any parameter changes. If the strategy still shows positive expectancy and acceptable drawdown, it has passed forward testing and may warrant small live trades.
Gap
A discontinuity in price between the close of one day (or bar) and the open of the next, usually caused by overnight news or economic events.
A stock closes at 50.00 on Friday and opens at 48.50 on Monday, creating a 1.50-point gap lower. Gaps create overnight risk for traders holding positions and opportunity for traders who specialize in gap reversals or gap continuations.
Hard Stop
An automated, non-negotiable stop-loss order placed at the time of entry to limit losses to a predetermined amount.
When you buy a stock at 50.00, you place a hard stop-loss order at 48.50 simultaneously; if the trade moves against you, the position is closed automatically at or near that level. A hard stop removes emotion and ensures losses stay within your plan.
High-Frequency Trading
Algorithmic trading strategies executed by institutions and hedge funds using powerful computers, often holding positions for milliseconds or microseconds.
HFT firms exploit tiny price discrepancies across exchanges or use statistical arbitrage, executing millions of trades per day. Retail traders cannot compete with HFT on speed or technology, but they can trade timeframes and setups where HFT is not active.
Iceberg Order
A large order split into smaller visible portions, with the remainder hidden until the visible portion is filled.
An institution wants to buy 1 million shares but places an iceberg order showing only 50,000 shares; as that 50,000 is filled, the next 50,000 becomes visible. Iceberg orders hide intent and prevent market impact, though they are illegal in some jurisdictions.
Kelly Criterion
A mathematical formula that calculates the optimal fraction of your account to risk on each trade, given your win rate and payoff ratio.
The Kelly formula is f = (bp − q) / b, where p is your win rate, q is your loss rate, and b is your payoff ratio. A trader with a 60 percent win rate and a 1:1 payoff should risk approximately 20 percent of the account per trade; risking more increases ruin risk, risking less leaves money on the table.
Level 2
A market data feed that shows the best bid and ask prices and the cumulative volume at each price level, revealing order flow structure.
On Level 2, you see that there is 100,000 shares offered at 50.10, 250,000 at 50.15, and 50,000 at 50.20. This visibility helps traders anticipate where buyers or sellers may emerge and whether a breakout is backed by sustained demand or a temporary spike.
Limit Order
An order to buy or sell a security at a specific price or better, which remains open until filled or cancelled.
You place a limit order to buy 100 shares at 49.95; your order enters a queue and only fills when the price reaches 49.95 or lower. Limit orders guarantee price but offer no guarantee of fill; in a fast market, the price may skip past your limit and never fill.
Liquidity
The ease and speed with which a security can be bought or sold in large size without causing significant price movement.
Apple stock has high liquidity—you can buy or sell 10,000 shares in seconds with minimal slippage. A micro-cap penny stock has low liquidity; selling a large position may require hours or days, and the price may move sharply against you as your sale absorbs available bids.
Mean Reversion
The tendency of prices to return to an average value after moving to an extreme, implying that large moves are often temporary.
A stock that trades at an average price of 50.00 but drops to 42.00 on panic selling is at an extreme; mean reversion traders bet that it will revert upward. Mean reversion works in choppy, range-bound markets but fails badly when a trend takes hold.
Momentum
The strength and direction of price movement, measured by rate of change, moving average slopes, or oscillators, indicating trend continuation.
A stock rising from 40 to 55 over three weeks has strong upward momentum; momentum traders seek to enter in the direction of that momentum and exit before it stalls. Momentum can persist longer than expected, but it always ends, stranding traders who enter near momentum peaks.
Monte Carlo Simulation
A statistical technique that randomly reshuffles past trades to create thousands of hypothetical trading histories, revealing the distribution of possible outcomes.
If you have 100 real trades with a 55 percent win rate, a Monte Carlo simulation might run 5,000 random permutations of those trades, showing that the worst-case 30-trade drawdown could be as deep as 40 percent. This reveals the full range of risk, not just the worst historical drawdown.
Opening Range
The price range established during the first period (usually the first hour) of a trading day, often serving as a support or resistance level.
A stock opens at 50.00 and trades between 49.95 and 50.50 in the first hour; that 0.55-point range is the opening range. Many professional day traders use the opening range as a framework for intraday support and resistance and for identifying breakout entries.
Order Flow
The real-time sequence of buy and sell orders hitting the market, visible through Level 2 data and tape reading, indicating institutional intent.
Seeing a series of large buy orders at the bid-ask spread followed by aggressive buying above the ask suggests accumulation; this order flow pattern often precedes a sustained rally. Order flow traders use this information to front-run larger moves.
Overtrading
Entering too many trades, too frequently, or with insufficient edge, often driven by boredom or the desire to "make back losses" quickly.
A trader with a single solid setup that triggers five times per week instead enters ten setups of mediocre quality, diluting edge and increasing transaction costs. Overtrading is the enemy of discipline; traders who overtrade often end quarters with negative returns despite being "in the market" constantly.
Paper Trading
Trading with simulated money in a live market environment to test a strategy or build skills without risking real capital.
A trader paper trades a new scalping setup for two weeks, taking twenty simulated trades, to confirm the strategy's edge before risking real money. Paper trading reveals whether discipline holds in live markets and whether fills match the assumptions made during backtesting.
Pattern Day Trader Rule
A Securities and Exchange Commission regulation requiring traders with accounts under $25,000 to limit day trades to three per rolling five-day period.
A retail trader with a $20,000 account who day trades four times in one week violates the rule and is subject to a trading suspension. Traders can circumvent this rule by maintaining $25,000 in equity or by swinging positions overnight, absorbing overnight risk in exchange for trading freedom.
Position Sizing
The practice of allocating a specific percentage of capital or number of shares to each trade based on account size and risk tolerance.
A trader with a $100,000 account who risks 1 percent per trade will risk $1,000 on each position. If the stop-loss is 100 shares × $10 away, the trader buys exactly 10 shares; if the stop is 50 shares × $10 away, the trader buys 20 shares. Proper position sizing ensures losses stay within plan.
Profit Factor
The ratio of gross profit to gross loss in a trading system, with values above 2.0 typically indicating a profitable system.
A strategy that wins $50,000 and loses $25,000 has a profit factor of 2.0. A profit factor below 1.5 is weak; above 3.0 is strong. Profit factor is useful for comparing strategies but does not account for drawdown or consistency.
Risk of Ruin
The probability that a trading account will be completely depleted by losses before the trader achieves profitability.
A trader risking 10 percent of the account per trade with a 45 percent win rate faces a high risk of ruin; even one unlucky streak can wipe the account. Risking 1 percent per trade with the same win rate lowers risk of ruin to near zero, allowing the edge to compound.
Scalping
A day trading strategy that enters and exits positions in seconds or minutes, capturing tiny price movements (ticks or cents) at high frequency.
A scalper might buy a liquid stock, hold for sixty seconds, and exit for a 0.05-cent profit; with a hundred scalps per day, these tiny gains compound. Scalping demands lightning-fast execution, low commissions, and the psychological resilience to accept small wins and small losses.
Setup
A specific, recurring pattern or condition in price or order flow that signals a high-probability opportunity to enter a trade.
A trader's setup might be "a stock closes above the twenty-day high with above-average volume on a breakout bar." When that setup appears, the trader enters with a predetermined stop and target. Setups are the foundation of repeatable, edge-based trading.
Slippage
The difference between the expected execution price and the actual fill price, usually caused by market movement or wide bid-ask spreads.
You submit a market order to sell at the current price of 50.05 but receive a fill at 49.95; the 0.10 slippage is the cost of slow execution or low liquidity. Slippage is especially harmful for scalpers, where tiny profits can be wiped out by a few cents of slippage.
Stop-Loss Order
An order to sell (or buy to cover) a position automatically if the price moves against the trader by a specified amount.
You buy a stock at 50.00 and place a stop-loss at 48.50; if the price falls to 48.50, your position is closed automatically. Stop-loss orders protect against catastrophic losses but can be triggered by whipsaws, wasting capital on false signals.
Swing Trading
A trading style that holds positions for days or weeks, capturing larger price swings than day traders while avoiding holding overnight risk on shorter timeframes.
A swing trader buys a stock showing bullish setup on Monday and sells on Friday after a 2-point gain; the trade captures a swing in price while riding a favorable technical setup. Swing trading tolerates larger intraday movements and benefits from overnight gaps.
Tape Reading
The practice of analyzing Level 2 data and time-and-sales order flow in real time to predict near-term price movement and identify accumulation or distribution.
A tape reader sees a series of large sell orders appearing at the bid but no aggressive buying; this signals distribution and predicts a price decline. Tape reading is a rare skill and demands years of screen time to develop.
Tilt
A psychological state in which a trader abandons their plan and makes emotional, revenge-driven trades after a loss or string of losses.
After three consecutive losses, a trader, now tilted, doubles position size on the next setup in an attempt to quickly recoup losses. Tilted trading is almost always unprofitable; the cure is stepping away from the screens.
VWAP
Volume-Weighted Average Price; the average price of a security weighted by trading volume, providing a benchmark for institutional execution.
An institution buying a large position wants to achieve a fill near VWAP; this level represents the "fair value" of the stock by volume. Intraday traders use VWAP as a dynamic support or resistance level, with price bounces from VWAP indicating institutional demand.
Win Rate
The percentage of trades that close at a profit, independent of the size of those profits or losses.
A strategy with a 55 percent win rate wins 55 out of every 100 trades on average. Win rate alone does not indicate profitability; a 55 percent win rate with an average win of $50 and average loss of $100 produces a negative expectancy.