Margin requirements refer to the minimum amount of funds that an investor must have in their account in order to buy securities on margin. This means that the investor is borrowing money from a brokerage firm or another financial institution to purchase the security, with the hope that its value will increase over time and they can then sell it for a profit, repaying the loan plus interest. The amount of funds required as collateral varies depending on the type of security being purchased, as well as market conditions. Margin requirements are set by regulatory bodies such as the Federal Reserve to protect investors from excessive leverage and potential losses.