what is margin 
in finance the margin is the collateral that an investor has to deposit with their broker or exchange to cover the credit risk the holder poses for the broker or the exchange for example a short position cannot be established without sufficient margin in the case of short sales under regulation t the federal reserve board requires all short sale accounts to have 150 of the value of the short sale at the time the sale is initiated the 150 consists of the full value of the short sale proceeds 100 plus an additional margin requirement of 50 of the value of the short sale 1