A call from a broker signaling the need for a trader to deposit additional money into a margin account to maintain a trade.
See Also:
Call: An Option contract that gives the holder the right to buy the underlying security at a specified price for a certain, fixed period of time.
Margin: A deposit contributed by a customer as a percentage of the current market value of the securities held in a margin account is thus the margin amount. This amount changes as the price of the investment changes. basicaly, margin is a buying a security by borrowing funds from a brokerage house.