A Margin Call happens when an investor’s margin account goes below the broker’s required amount. The Margin Account of an investor has securities bought through money lent (by the investor’s broker).
A Margin Call is held as an indicator that one or more of the securities held in the Margin Account had gone down in value. Once a Margin Call happens, the investor is compelled to choose between depositing money in the account or selling some of the assets that is within their account.
Margin Calls are effectively demands for capital or securities to be added upon so as to get a Margin Account to the minimum maintenance margin.