Equity Markets and Stock Instruments › Equity Markets and Stock Instruments

A stock quote can show an ask of $100, yet a 1,000-share purchase can cost more than$100 per share. In the order-book example below, the average fill is $100.035 because the order exhausts the cheapest displayed shares. Understanding what you own, where an order can execute and how returns are measured helps you distinguish a trading opportunity from a misleading price or valuation comparison.

For quantitative finance practitioners, equity markets offer rich data streams: prices, volumes, order flows, and corporate financials. These data form the raw material for building trading strategies, risk models, and portfolio optimization systems. Before diving into sophisticated modeling techniques in later chapters, you need a solid understanding of what stocks represent, how they trade, and what drives their returns.

This chapter builds your foundational knowledge of equity markets. We start with the nature of stock ownership, move through market structure and trading mechanics, and conclude with the key metrics that quantitative analysts use to characterize individual stocks and portfolios.