Collateral that the holder of a position in securities, options, Forex or futures contracts, has to deposit to cover the credit risk of his counterparty. Other definitions to MARGIN, used in other areas are: (1) Difference between the buying and selling rates, also used to indicate the discount or premium between spot or forward. (2) For options, the sum required as collateral from the writer of an option. (3) For futures, a deposit made to the clearing house on establishing a futures position account. (4) The percentage reserve required by the US Federal Reserve to make an initial credit transaction.