Margin

From Reuters Financial Glossary

Margin allows trading without having the full amount of funds available. It is a part-payment of collateral to cover contractual obligations and to insure against potential unlimited loss. Clearing houses in futures markets demand an initial margin from both the buyer and the seller of a futures contract to ensure they will be able to meet their contractual obligations. To ensure that margin requirements keep pace with subsequent market movements, variation margin is also called for. This is calculated by revaluing all positions with reference to the closing prices each day.

See also: Margin