Deposit deposited by an investor when purchasing securities. The margin payment is designed to represent the maximum possible shift in the value of the security in the market. If prices begin to fall sharply, the broker may be called upon to increase the deposit. Margin may also be: a) the difference between the bank lending rate and the deposit rate, b) additional collateral to cover any decline in the value of the collateral (security) of the loan, c) money given as a guarantee that the contract will be fulfilled.