Option-adjusted Spread, or OAS, is one of the most important valuation tools in fixed income when a bond’s cash flows can change because of embedded options. It helps investors strip out the effect of those options and estimate the spread they are really earning for non-option risks such as credit, liquidity, and structure. If you compare callable bonds, putable bonds, or mortgage-backed securities, understanding OAS is essential.

Option-adjusted Spread (OAS) is a core fixed-income measure used to compare bonds and structured products that contain embedded options such as calls, puts, or mortgage prepayment features. In simple terms, OAS tries to show the extra spread an investor earns after removing the effect of those options through a pricing model. If you want to analyze callable bonds, mortgage-backed securities, or relative value in debt markets, understanding OAS is essential.

An option is a derivative contract that gives the buyer a right, but not an obligation, to buy or sell an underlying asset at a predetermined price within a defined period. That simple feature makes options one of the most flexible tools in markets: they can hedge risk, create leveraged exposure, generate income, or express a view on volatility rather than only direction. To use options well, you must understand not just calls and puts, but also premiums, strikes, time decay, volatility, settlement, and regulation.

An Opening Auction is the exchange process that sets the first tradable price of a security for the day by pooling buy and sell orders before continuous trading begins. Instead of matching orders one by one at the opening bell, the market gathers interest, calculates a clearing price, and executes as much eligible volume as possible at that single price. Understanding the Opening Auction helps traders, investors, students, and market professionals interpret opening gaps, order imbalances, and early-session liquidity.

Open Interest is one of the most useful numbers in derivatives trading, but it is also one of the most misunderstood. In futures and options, it tells you how many contracts are still active, which helps you judge participation, liquidity, and whether fresh positions are building up or getting closed. If you learn to read open interest along with price and volume, you gain a much clearer view of market behavior.

In fixed income markets, an **on-the-run** bond is the most recently issued bond or note in a given maturity segment, most commonly a government security such as a U.S. Treasury or a benchmark government bond in another country. Because it is the newest and usually the most actively traded issue, it often becomes the market’s preferred reference point for pricing, hedging, and measuring liquidity. Understanding **on-the-run** versus **off-the-run** is essential for bond trading, yield-curve analysis, and relative-value investing.

Off-the-run refers to a bond issue that is no longer the most recently issued security in its maturity segment. In practice, the term is used most often in government bond markets, especially U.S. Treasuries, where off-the-run bonds usually trade less actively and often at slightly higher yields than the current benchmark issue. Understanding off-the-run securities is important because they affect liquidity, pricing, execution costs, hedging, and relative-value trading.

An **Off-book Trade** is a market transaction executed outside an exchange’s central visible order book. That does **not** automatically make it improper or secret; in many markets it is a normal way to handle block orders, dealer-led bond trades, negotiated transactions, or off-exchange executions that are still reported under regulatory rules. Understanding off-book trading is essential if you want to interpret liquidity, transparency, execution quality, and market structure correctly.

The **OPEC Basket** is one of the most practical reference prices in the oil market because it compresses the value of a range of OPEC crude streams into one number. For beginners, it is the average price signal for representative OPEC oil; for professionals, it is a tool for analyzing exporter revenues, importer costs, energy stocks, inflation, and policy decisions. If you want to understand how OPEC-related price moves affect markets, the OPEC Basket is a strong place to start.

Novation is a foundational post-trade concept in market structure because it changes who legally stands behind a contract. In cleared markets, novation typically means the original trade between buyer and seller is replaced by new contracts involving a central counterparty, or CCP; in bilateral markets, it can mean transferring a contract from one party to another with consent. If you want to understand clearing, counterparty risk, settlement, and modern derivatives regulation, you need to understand novation.

A **Non-deliverable Forward (NDF)** is a foreign-exchange derivative used to lock in an exchange rate without actually delivering the underlying restricted currency. Instead, the two parties settle the gain or loss in cash, usually in a freely usable currency such as US dollars. NDFs matter most in emerging-market and controlled-currency environments, where investors, corporates, and banks need currency protection but cannot easily access the onshore deliverable market.

An NDF, or Non-deliverable Forward, is a foreign exchange derivative that lets two parties lock in an exchange rate today and settle the gain or loss later in cash, usually without delivering the underlying currencies. It is especially important for currencies that are restricted, not freely deliverable offshore, or difficult to access across borders. If you want to understand how companies, banks, funds, and analysts manage offshore currency risk, the Non-deliverable Forward is one of the most important instruments to know.

A **Non-cleared Derivative** is a derivative contract that is **not** cleared through a central counterparty, so the two original parties remain directly exposed to each other. In practical terms, that means the trade stays as a direct bilateral obligation between the counterparties rather than being transferred, or **novated**, to a clearinghouse.

Netting is the process of combining multiple obligations and replacing them with one final amount to pay, receive, deliver, or settle. In market structure, that simple idea is a core engine of modern trading, clearing, derivatives, and payment systems. If you understand netting, you understand how markets reduce transaction volume, funding pressure, and counterparty exposure—while still leaving important legal, liquidity, and operational risks to manage.

A **Negative Covenant** is a promise in a bond indenture or loan agreement that the borrower or issuer will **not** do certain things unless agreed conditions are met. In fixed income markets, these clauses protect lenders and bondholders from actions that could weaken credit quality, reduce recovery value, or shift risk after the money has already been raised. If you understand negative covenants well, you can read debt documents more intelligently, compare bond risk more accurately, and make better issuance, lending, and investment decisions.

Natural Gas Liquids, often shortened to NGLs, are valuable hydrocarbon liquids separated from raw natural gas. They sit at the intersection of gas production, petrochemicals, heating fuels, refining, exports, and midstream infrastructure. Understanding natural gas liquids helps explain why two gas fields with similar gas output can have very different economics.

National Best Bid and Offer, usually shortened to **NBBO**, is one of the most important reference points in modern market structure. It tells you the highest publicly displayed buy price and the lowest publicly displayed sell price available across the consolidated market for a security at a given moment. If you trade stocks or options, evaluate broker execution quality, or study how fragmented markets work, understanding the NBBO is essential.

NBBO, or National Best Bid and Offer, is the U.S. market’s consolidated view of the best displayed buy price and best displayed sell price for a security across trading venues. If you trade stocks, route orders, review execution quality, or study market structure, NBBO is a foundational concept. It sits at the center of best execution, smart order routing, and the practical realities of fragmented electronic markets.

Municipal Bond refers to debt issued by a state, city, local authority, or similar public entity to fund public projects such as schools, roads, water systems, and hospitals. In fixed income markets, municipal bonds matter because investors evaluate them not only by coupon and maturity, but also by credit quality, tax treatment, call features, and public-finance fundamentals. If you understand municipal bonds, you understand a major bridge between capital markets and real-world infrastructure.

A Multilateral Trading Facility, or MTF, is a rules-based trading venue that brings together multiple buyers and sellers of financial instruments. It is most important in European and UK market structure, where it sits alongside regulated markets, organized trading facilities, and bilateral OTC trading. If you want to understand how modern orders are routed, executed, and monitored outside a traditional stock exchange model, you need to understand the MTF.

An **MTF**, or **Multilateral Trading Facility**, is a trading venue where multiple buyers and sellers can meet and trade financial instruments under a defined rulebook. It is a core concept in modern market structure, especially in Europe and the UK, where MTFs compete with traditional exchanges and influence liquidity, spreads, and execution quality. In some countries, especially India, **MTF** can also mean **Margin Trading Facility**, but in this tutorial the term means **Multilateral Trading Facility**.

Mortgage-backed Security (MBS) is a fixed-income instrument created by pooling mortgage loans and passing the borrowers’ payments through to investors. It is one of the most important links between housing finance and the bond market. If you understand how an MBS works, you understand how lenders fund mortgages, how investors earn yield from housing-related debt, and why interest-rate changes affect this market differently from ordinary bonds.

MBS usually means **Mortgage-backed Security**, a major instrument in the fixed income and debt markets. It represents a claim on cash flows from a pool of mortgage loans, so investors are effectively paid from homeowners’ principal and interest payments. Understanding MBS matters because it sits at the intersection of housing finance, bond investing, bank funding, interest-rate risk, and financial regulation.