A margin call is a demand from a broker to an investor to deposit additional funds or securities into their account when the margin balance falls below a certain level. Margin is the amount of money an investor borrows from a broker to buy securities. If the value of the securities in the account falls below a certain level, the broker may issue a margin call to the investor, requiring them to deposit more funds or securities to cover the shortfall. Failure to meet a margin call can result in the broker selling securities in the account to raise cash to meet the margin requirement.