Legal Definition of Margin:  The actual amount of money one must pay toward the purchase of a stock when buying on margin. Such sum is only part of the total cost of the security, with the broker having the right to receive the balance should the value of the stock decline markedly | Learn the legal definition of margin in stock trading and understand its implications for your investments. Find out how buying on margin can increase your returns, but also carries higher risks. Discover the broker’s right to receive the balance and learn how to navigate the stock market confidently