Margin Call
Also known as: Stop-Out
A margin call is the broker's alert that your account equity has dropped close to the minimum needed to support your open positions. Specifically, it fires when margin level (equity / used margin) falls below the broker's margin-call threshold — typically 100% or 50%.
Ignoring a margin call leads to a stop-out: the broker automatically closes losing positions, starting with the largest, until margin level recovers. Stop-out levels are commonly set 20-50 percentage points below margin-call levels.