A file extension is the characters after the last dot in a file name. For example, in the file name winmail.dat, the file extension is dat. It helps Windows select the right program to open the file.
Margin is borrowing money from your broker to buy a stock and using your investment as collateral. Investors generally use margin to increase their purchasing power so that they can own more stock without fully paying for it.But margin exposes investors to the potential for higher losses.ut if you bought the stock on margin  paying $25 in cash and borrowing $25 from your broker  you'll earn a 100 percent return on the money you invested. Of course, you'll still owe your firm $25 plus interest.
After you buy stock on margin, FINRA requires you to keep a minimum amount of equity in your margin account. The equity in your account is the value of your securities less how much you owe to your brokerage firm. The rules require you to have at least 25 percent of the total market value of the securities in your margin account at all times.