Trading Terminology Glossary

Trading Terminology Glossary

This reference glossary defines core financial trading terms, market microstructure concepts, order types, routing algorithms, position accounting metrics, risk controls, and system architecture terminology used across the Emporia Trading Platform.

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🏷️ Quick Index

• 1. Order Types & Time-in-Force
• 2. Market Microstructure & Order Book
• 3. Order Routing & Execution Strategies
• 4. Positions, Accounting & PnL
• 5. Risk Management & Market Controls
• 6. System Architecture & Protocol Terms

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1. Order Types & Time-in-Force

Order Types

• Market Order: An order to buy or sell a stock immediately at the best available prevailing market price. Guarantees execution speed over price level.
• Limit Order: An order to buy or sell at a specified maximum (for buy) or minimum (for sell) limit price. Guarantees price bounds but does not guarantee immediate execution.
• Stop-Loss Order: An order that becomes an active market or limit order once a specified trigger price (stop price) is reached, used to limit downside loss.
• Take-Profit Order: An order set at a target price level to automatically close an open position once a specified profit target is hit.

Time-in-Force (TIF)

• DAY (Day Order): An order valid until the end of the current trading day. Automatically cancelled if unexecuted at market close.
• IOC (Immediate-or-Cancel): An order requiring immediate execution of all or part of the quantity upon reaching the venue; any unexecuted portion is immediately cancelled.
• FOK (Fill-or-Kill): An order requiring the entire quantity to be filled immediately in full; if not fully filled, the entire order is cancelled (no partial fills).
• GTC (Good-Till-Cancelled): An order that remains active in the order book across multiple trading days until explicitly executed or manually cancelled.

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2. Market Microstructure & Order Book

• Bid: The highest price a buyer is willing to pay for a stock.
• Ask (Offer): The lowest price a seller is willing to accept for a stock.
• Spread (Bid-Ask Spread): The price difference between Best Ask and Best Bid: Spread = P_ask - P_bid.
• BBO (Best Bid and Offer): The top-of-book highest bid and lowest ask price for a specific exchange venue.
• NBBO (National Best Bid and Offer): The consolidated best bid and best ask price calculated across all regulated exchange venues in a jurisdiction.
• Level 1 (L1) Data: Real-time market feed containing top-of-book BBO price, quote sizes, and latest trade price.
• Level 2 (L2) Data: Order book depth feed showing resting order quantities aggregated across multiple price levels (typically top 5–10 bids and asks).
• Price-Time Priority (FIFO): Queue priority matching rule where resting orders at the best price are filled first; orders at the same price are matched in order of arrival timestamp.
• Tick Size: Minimum price increment allowed for an instrument (e.g., $0.01 for U.S. equities).
• Size Increment (Lot Size): Minimum share quantity increment for orders (e.g., 1 share or 100-share round lots).
• Mid-Price: Simple midpoint average between Best Bid and Best Ask: P_mid = (P_bid + P_ask) / 2.
• Micro-Price: Volume-weighted mid-price adjusting for order book depth imbalance: P_micro = ((Q_bid × P_ask) + (Q_ask × P_bid)) / (Q_bid + Q_ask).

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3. Order Routing & Execution Strategies

• DMA (Direct Market Access): Orders routed directly to a specific execution venue or matching engine without intermediary algorithm intervention.
• SOR (Smart Order Router): An algorithmic router that scans multiple liquidity venues to route orders to the venue displaying the NBBO price.
• VWAP (Volume-Weighted Average Price): An execution strategy that slices large parent orders into child orders scheduled across intraday time intervals to match historical volume profiles.
• TWAP (Time-Weighted Average Price): An execution strategy that divides parent orders into equal child slices released at uniform time intervals.
• Matching Engine: High-frequency software system (such as Emporia's exchange-core) that matches buy and sell orders using lock-free data structures (e.g., LMAX Disruptor).
• Slippage: The difference between an order's expected price (or submission price) and the actual executed trade price due to fast-moving market prices.

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4. Positions, Accounting & PnL

• Long Position: Holding a positive quantity of shares (Q > 0). Profitable when asset price rises.
• Short Position: Holding a negative position quantity (Q < 0) by borrowing shares to sell. Profitable when asset price declines.
• Flat Position: Holding zero net position (Q = 0).
• Cost Basis: The volume-weighted average purchase price per share of an open position: CostBasis_new = ((CostBasis_prev × Q_prev) + (P_fill × Q_fill)) / (Q_prev + Q_fill).
• Realized PnL: Locked-in profit or loss realized when closing or reducing an open position.
• Unrealized PnL (Mark-to-Market): Paper profit or loss calculated on open positions against current market quotes (P_mark).
• Buying Power: Account cash plus available margin leverage representing maximum order purchasing capacity.

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5. Risk Management & Market Controls

• Price Collar (Fat-Finger Guard): Permitted price band surrounding current market quotes (lowerBand <= P_limit <= upperBand) to reject erroneous order entries.
• Position Limit: Maximum net share quantity or total exposure value permitted per instrument symbol.
• Max Order Value Limit: Maximum monetary value allowed for a single order submission (e.g., max $100,000).
• Circuit Breaker: Regulatory or exchange mechanism that halts trading temporarily during extreme market volatility.

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6. System Architecture & Protocol Terms

• CQRS (Command Query Responsibility Segregation): Architectural pattern separating write-side command operations (order-command-service & OMS) from read-side query projections (REST & SSE streams).
• Event-Driven Architecture (EDA): System design paradigm where state changes trigger immutable asynchronous Kafka domain events (emporia.orders.v1).
• Idempotency: Property where executing an operation multiple times (e.g., command retry via ProcessedCommandRepository) produces the exact same outcome without duplicate side-effects.
• FIX Protocol (Financial Information eXchange): International messaging standard for electronic institutional trading (FixExecutionVenueGateway).
• Disruptor (LMAX Disruptor): Ultra-low latency lock-free ring-buffer concurrency framework for inter-thread messaging used in high-performance matching engines (exchange-core).
• Quote Conflation: Merging high-frequency quote updates within a conflation window (e.g., 250ms) to emit only the latest state to subscribers, preventing queue backpressure.