A demand from a broker to an investor for additional money or securities to bring an account back up to the required margin level.
A margin call is a demand from a broker for an investor to deposit additional funds or securities into their margin account when the account equity falls below a certain maintenance margin level. This situation arises when an investor has borrowed money from the broker to purchase securities, and the value of those securities has declined. Failure to meet a margin call can result in the broker liquidating the investor's holdings to cover the shortfall.