A broker notification that account equity has fallen below the required margin level, prompting deposit or trade closure.
When floating losses erode equity to the point where used margin exceeds a broker's maintenance threshold, the broker issues a margin call. If equity continues to fall to the stop-out level, the broker automatically closes the largest losing positions to restore margin.
Margin call and stop-out levels vary by broker and are quoted as a percentage of required margin. Understanding these thresholds is essential for sizing positions safely.