Margin call in forex trading occurs when a trader's account balance falls below the required margin level. This can happen due to market volatility, unexpected news, or poor trading decisions. Margin is a double-edged sword that can amplify both profits and losses, so it's important for traders to use risk management strategies and maintain adequate margin levels. Failure to do so can lead to margin calls, which require additional funds to be deposited or trades to be closed, potentially resulting in further losses.