Margin

Margin in trading refers to the practice of borrowing money from a broker, bank, or exchange to purchase stocks or other securities. Margin trading allows investors to buy more stock than their cash balance would normally permit by borrowing. This leverage can significantly increase both gains and losses. Investors with margin must maintain a minimum margin requirement; falling below this can trigger a margin call. During a margin call, one must deposit more funds or sell investments to cover the shortfall, or the lender might forcibly sell assets from the account.
Because using margin is a form of borrowing money it comes with costs, and marginable securities in the account are collateral. The primary cost is the interest you have to pay on your loan. The interest charges are applied to your account unless you decide to make payments. Over time, your debt level increases as interest charges accrue against you. As debt increases, the interest charges increase, and so on. Therefore, buying on margin is mainly used for short-term investments. The longer you hold an investment, the greater the return that is needed to break even. If you hold an investment on margin for a long period of time, the odds that you will make a profit are stacked against you.