The Stop Out Level is when your Margin Level falls to a specific percentage (100%) level in which one or all of your open positions are closed automatically (“liquidated”) by your broker. This liquidation happens because the trading account can no longer support the open positions due to a lack of margin.
More specifically, the Stop Out Level is when the Equity is lower than a specific percentage of your Used Margin. If this level is reached, your broker will automatically start closing out your trades starting with the most unprofitable one until your Margin Level is back above the Stop Out Level.
To calculate the margin level, you must divide the available equity by the used margin and put it in percentages: (available equity/used margins) x 100%
If the margin level is above 100%, a trader can open new trades. But, if the margin level goes below 100%, the broker will start "stopping out" of the current positions.