Margin Account

In a margin account, your brokerage firm can lend you money to buy securities, with the securities in your portfolio serving as collateral for the loan. As with any other loan, you will incur interest costs when you buy securities on margin. There are risks from purchasing securities on margin that do not come with most other types of loans. For example, if the value of your securities declines significantly, you may be subject to a "margin call."

Source: http://investor.gov/glossary/glossary_terms/margin-account#.Us7e6mRDuEg