Market Maker is one of the most important terms in market structure because it explains who provides tradable prices when other participants want to buy or sell. In both exchange-traded and over-the-counter markets, a market maker helps create liquidity, supports price discovery, and reduces the friction of trading. If you understand how a market maker works, you can better interpret spreads, execution quality, volatility, and the real cost of entering or exiting a position.

Market Impact is the effect a trade has on the market price of the security being traded. In simple terms, if you try to buy a lot very quickly, you may push the price up; if you try to sell a lot quickly, you may push it down. Understanding market impact is essential in market structure and trading because it shapes execution cost, liquidity planning, best execution decisions, and how professionals break large orders into smaller pieces.

Market Depth shows how much buying and selling interest exists at different price levels, not just at the current best bid and best ask. It is one of the most useful market-structure concepts because it helps explain liquidity, slippage, market impact, and execution quality. In simple terms, market depth tells you how much size the market can absorb before price starts moving materially.

A **market** is more than a place where buyers and sellers meet. In market structure and trading, it is the full system of venues, participants, rules, prices, orders, and post-trade processes that make trading possible. Understanding what a market is helps you read price action better, choose the right execution method, and understand how regulation, liquidity, and settlement shape real-world trading outcomes.

Mark-to-market is the practice of valuing a position at current market prices instead of the original transaction price. In derivatives, it is especially important because futures and many risk systems reprice positions every day, changing profit and loss, collateral needs, and risk exposure in real time. Understanding mark-to-market helps traders, hedgers, treasurers, accountants, investors, and regulators see the current economic value of a position rather than waiting until final settlement.

Mark Price is one of the most important prices in modern markets because it is often the price that risk systems, brokers, exchanges, and counterparties actually use—even when it is not the last traded price. In derivatives, options, and many OTC products, Mark Price helps estimate fair value, calculate unrealized profit and loss, manage margin, and reduce distortion from isolated or manipulated trades. If you have ever wondered why your trading screen, P&L, and liquidation level do not line up with the latest trade, Mark Price is usually the reason.

Margin requirement is the minimum collateral a trader, hedger, or institution must post to open and maintain certain derivatives positions. In plain language, it is a financial safety buffer designed to absorb potential losses and reduce counterparty risk. In derivatives and hedging, understanding margin requirement is essential because a good trade or hedge can still fail if the cash needed to support it is not planned properly.

The **maker-taker model** is a market-structure pricing system in which a trading venue rewards participants who add liquidity and charges those who remove it. It matters because it influences spreads, order routing, execution quality, exchange competition, and even regulatory debates about fairness and best execution. If you trade, route orders, study market microstructure, or evaluate brokers and exchanges, this is a core concept to understand.

Maker Fee is the charge or pricing adjustment tied to orders that add liquidity to a trading venue instead of immediately consuming existing liquidity. Understanding a maker fee helps traders, investors, brokers, and market-structure learners estimate true trading cost, compare venues intelligently, and avoid the common mistake of focusing only on headline commissions. In some markets the maker side pays a small fee, while in others the maker side may receive a rebate.

A **Make-whole Provision** is a debt redemption clause that lets an issuer repay a bond or other debt before maturity, but only after paying investors an amount designed to compensate them for the cash flows they lose. In simple terms, the issuer can exit early, but usually only by paying a premium based on the present value of the remaining coupons and principal. This matters in fixed income and debt markets because it affects bond pricing, call risk, refinancing decisions, portfolio returns, and capital structure strategy.

Macaulay Duration is one of the most important concepts in fixed income because it turns a bond’s stream of future cash flows into a single, usable number. In plain English, it tells you the weighted average time it takes to get your money back from a bond, considering both coupon payments and principal repayment. It also serves as the foundation for understanding interest-rate risk, portfolio immunization, and many professional bond analytics.

Lot Size is the standardized quantity of the underlying asset represented by one derivatives contract. In futures and options markets, it determines the minimum tradable contract quantity, the exposure per contract, and the scale of profit, loss, margin, and hedging. If you misunderstand lot size, you can easily misread the true risk of a trade by a large amount.

A **Locked Market** is a market-structure condition in which the best bid equals the best ask for the same security. In plain language, buyers and sellers are both quoting the same price, so the displayed spread is zero. That may look efficient, but in real trading it can reflect intense competition, quote timing issues, fragmented venues, or rule-driven order handling.

A **Lit Market** is the visible part of trading where prices, quotes, or resting orders are displayed before trades happen. In plain English, it is the “open screen” of the market, where buyers and sellers can see available prices instead of negotiating entirely in private. Understanding lit markets is essential for anyone studying market structure, execution quality, liquidity, transparency, or price discovery.

A liquidity vacuum happens when buyers, sellers, or quoted orders suddenly disappear from the market, leaving too little depth to absorb trades smoothly. When that happens, prices can jump or fall much more than expected, spreads widen, and executions become costly. Understanding a liquidity vacuum helps traders, investors, businesses, and regulators distinguish a genuine information-driven move from a move amplified by missing liquidity.

A liquidity provider is a market participant that helps other people trade by standing ready to buy, sell, or quote prices in a financial instrument. In market structure, liquidity providers are central to order handling, price discovery, trade execution, and sometimes the ability of a market to function smoothly during normal conditions. If you understand what a liquidity provider does, you can better interpret spreads, execution quality, trading costs, and market resilience.

A Limit-if-touched Order On Open is a conditional trading instruction that combines a trigger price, a limit price, and an opening-only execution window. It is designed for traders who want to participate in the market open only if price reaches a chosen level first, while still controlling the worst acceptable execution price. Because brokers and exchanges do not all implement this order the same way, understanding the mechanics is essential before using it.

A **Limit-if-touched Order On Close** combines two ideas: a price trigger and an end-of-day execution instruction. The order stays inactive until the market touches a chosen price and, if broker or venue rules allow, it then becomes a limit order intended for the market close or closing auction. Because this combination is not standardized across all brokers and exchanges, understanding the trigger logic, cut-off times, and differences from a plain limit-on-close order is essential.

A **Limit-if-touched Order GTT** is a standing trading instruction that waits for a chosen price to be touched and then places a limit order. Traders and investors use it to automate a **buy-on-dip** or **sell-on-rise** decision without watching the screen all day. The idea is simple, but the details—trigger price, limit price, broker handling, and fill risk—are what determine whether it works well in practice.

A **Limit-if-touched Order GTD** is a conditional trading instruction that becomes a limit order only if the market reaches a chosen trigger price, and it remains valid only until a specified date. Traders use it to buy on a dip or sell on a rally without watching the screen all day. It is useful for disciplined execution, but it does **not** guarantee a fill once triggered.

A **Limit-if-touched Order GTC** is a conditional trading instruction that waits for price to reach a chosen level and then turns into a **limit order** that can stay active until you cancel it. Traders use it to buy on pullbacks or sell on rallies without watching the market every minute. The concept is simple, but the details—trigger price, limit price, fill rules, and broker-specific GTC expiration—matter a lot.

A **Limit-if-touched Order Extended Hours** is a conditional trading instruction that waits for a specified price to be reached during pre-market or after-hours trading and then sends a limit order. It is designed for traders who want to react to off-hours price moves without giving up price control. The catch is important: in extended hours, liquidity is thinner, spreads are wider, and broker handling can vary, so a trigger does **not** guarantee execution.

A **Limit-if-touched Order Day** is a contingent trading instruction that becomes a **limit order only if a specified trigger price is touched during the current trading day**. It combines two ideas: an **if-touched trigger** and **day-only validity**. Traders use it when they want a controlled entry or exit if price reaches a target intraday, without leaving a live limit order exposed for the whole session.

A **Limit-if-touched Order At Open** is a specialized trading instruction that combines a price trigger with an opening-only execution window. In simple terms, it tells the broker or trading system: *“Activate my limit order only if price reaches this level at or into the market open.”* It matters because the open is often the most volatile part of the trading day, and traders use this order logic to control both **when** they participate and **the worst price** they are willing to accept.

A **Limit-if-touched Order At Close** is a hybrid trading instruction that combines a price trigger with an end-of-day execution constraint. In plain language, the order becomes active only if the market touches a chosen price, and it is meant to work around the market close—often the closing auction or, on some platforms, only until the session ends. Because brokers and exchanges do not always implement this exact label the same way, understanding the mechanics before placing the order is essential.

Limit-if-touched Order After Hours is a conditional trading instruction used outside the regular market session to convert a price trigger into a limit order. It helps traders buy on a dip or sell on a rally after the close without giving up price control. Because after-hours markets are often thinner, wider, and faster than regular trading, this order type is useful only when you clearly understand how the trigger, limit price, and session rules work on your broker’s platform.

Limit Up-Limit Down is a market structure safeguard designed to stop trades from happening at prices that are too far away from a stock’s recent trading level. In fast-moving markets, it creates a moving price band around the market and can trigger a short trading pause if buying or selling pressure becomes extreme. For traders, investors, brokers, and exam candidates, understanding Limit Up-Limit Down is essential for order placement, volatility control, and interpreting sudden trading interruptions.

A **Limit Order On Open** is a trading instruction to buy or sell a security at the market open, but only at a specified price or better. It combines two ideas: **timing** (execute at the opening auction or opening trade) and **price protection** (do not execute beyond the limit price). This order type matters because the opening minutes can be volatile, and traders often want access to opening liquidity without giving up control over price.

A **Limit Order On Close** is a trading instruction to buy or sell only in the market’s closing auction, and only at a price that meets your stated limit or better. It is designed for traders and investors who care about the official closing price but still want price protection. In practice, it is one of the clearest examples of how *timing* and *price control* can be combined in a single order type.

A **Limit Order GTT** is a standing trading instruction that waits for a price trigger and then places a **limit order**. It is useful when you want to plan an entry or exit in advance without watching the screen all day. The key benefit is discipline and automation; the key caution is that **triggering does not guarantee execution**.