In market structure, the **ask** is the price at which a seller is willing to sell a security, currency, or other instrument right now. If you want to buy immediately, you usually trade at the current ask or across multiple ask levels if the available quantity is small. Understanding the ask is essential because it affects execution price, trading cost, liquidity analysis, and best-execution decisions in both exchange-traded and OTC markets.

An Asian option is an option whose payoff depends on the average price of an underlying asset over a period, not just the price on one expiration date. That single design change makes it especially useful for hedging fuel, commodities, currencies, and other exposures that build up over time rather than all at once. A business that buys fuel every day, receives foreign currency in batches, or settles against a monthly commodity index often cares far more about the average price over the month than about the price at one closing bell.

An **American Option** is an option contract that can be exercised **at any time up to and including its expiration date**. That one feature—early exercise—changes how the option is valued, how traders hedge it, and when it may make sense to use it instead of a European-style option. If you understand American options well, you understand a major part of real-world derivatives, especially listed equity options and many practical hedging decisions.

An **Alternative Trading System (ATS)** is a trading venue that matches or facilitates securities trades outside a traditional stock exchange. It matters because a meaningful share of modern trading in equities, bonds, and other instruments happens off-exchange, often to reduce market impact, improve anonymity, or access specialized liquidity. If you want to understand market structure, order routing, dark pools, execution quality, and best execution, you need to understand how an ATS works.

ATS stands for **Alternative Trading System**, a non-exchange venue where securities can be bought and sold. In modern market structure, ATSs sit between traditional exchanges and purely bilateral trading, giving brokers and institutional investors additional ways to find liquidity, reduce market impact, or keep orders less visible. If you hear terms like *dark pool*, *ECN*, *off-exchange execution*, or *smart order routing*, you are already close to the ATS ecosystem. This guide explains what an ATS is, why it exists, how it works, and how professionals evaluate when to use one.

All-or-None (AON) is an order instruction that requires a trade to be executed in full or not executed at all. It is most useful when a partial fill would create inconvenience, execution risk, or an unwanted leftover position. In market structure and trading, understanding All-or-None helps you choose the right order type, set realistic execution expectations, and avoid confusing it with similar instructions like Fill-or-Kill.

Algorithmic trading is the use of computer-defined rules to place, route, manage, or execute trades with limited manual intervention. It is a core part of modern market structure, spanning stock exchanges, futures markets, options, FX, bonds, and many OTC workflows. In practice, algorithmic trading includes everything from simple order-slicing tools like VWAP and TWAP to advanced market-making, statistical arbitrage, and automated hedging systems.

Algorithmic Trading, often called **Algo Trading** or **Algo-Trading**, means using computer-coded rules to place, manage, or execute trades in financial markets. It can be as simple as a moving-average strategy on a retail platform or as advanced as an institutional execution engine that slices a large order across multiple venues. Understanding it matters because modern market structure, liquidity, execution quality, and trading risk are increasingly shaped by algorithms.

Agricultural commodity refers to a farm-derived raw product such as wheat, corn, cotton, coffee, sugar, soybeans, or livestock that is produced, stored, moved, processed, and traded in physical and derivative markets. It is one of the most important concepts in commodity markets because it connects weather, food supply, inflation, trade flows, farmer income, and corporate costs. If you understand how an agricultural commodity works, you can better analyze prices, hedging, procurement, policy risk, and investment exposure.

An **agency bond** is a debt security issued by a government agency or a government-sponsored enterprise, most commonly discussed in the U.S. fixed-income market. It often offers a higher yield than a comparable Treasury, but its legal backing, liquidity, and call features can be very different. If you want to understand bond-market risk beyond simple “safe vs risky” labels, agency bonds are one of the best places to start.

Affirmation is a post-trade market process in which the parties, or their agents, agree that the details of an executed trade are correct and can move toward settlement. It sounds administrative, but it is central to modern market structure because a trade that is not properly affirmed can turn into a settlement break, a failed delivery, extra cost, or an avoidable operational risk. In short, affirmation is where “we traded” becomes “we agree on exactly what we traded.”

Adverse Selection is a core market microstructure concept that explains why getting a trade done is not always a win. In trading, it means you may be dealing with someone who knows more than you do, so your order gets filled just before the price moves against you. Understanding adverse selection helps explain bid-ask spreads, execution quality, market-maker behavior, and why some order flow is considered more “toxic” than others.

Accrued interest is the portion of a bond’s coupon that has built up day by day since the last payment date, even though the cash has not yet been paid. It matters because most bonds trade between coupon dates, so buyers and sellers need a fair way to split the next coupon payment. If you understand accrued interest, you understand why a bond’s quoted price is often not the same as the cash amount you actually pay.