A line of credit from a broker that provides an investor with capital for the purpose of purchasing securities. The loan usually finances up to 50% of the securities purchase and is secured by stock owned by the client. Hedge funds can usually leverage themselves far more than that through other means, such as joint back offices. Like any form of leverage, a margin loan allows investors to boost their buying power, while at the same time increasing their risk. The value of the securities an investor holds in a margin account must be maintained above a minimum level in order for the loan to remain in good standing. If the value of the collateral falls below the threshold, the investor will get a margin call, also known as a Regulation T (Reg T) call.