A stock exchange is a marketplace where shares of publicly traded companies are bought and sold. It provides a platform for investors to trade stocks, allowing them to buy ownership in companies and sell their shares to others. The prices of these shares fluctuate based on supply and demand, reflecting the company's performance and market conditions. Major stock exchanges, such as the New York Stock Exchange (NYSE) and the NASDAQ, facilitate these transactions and ensure fair trading practices. They also provide important information, such as stock prices and trading volumes, helping investors make informed decisions about their investments.