The lowest low value is the lowest low observed over a number of periods. The default period is set to 14, but that parameter can easily be changed in StockChartsACP.
The Lowest Low Value indicator is plotted as an overlay on the price chart.
If price moves below or touches the Lowest Low Value indicator it could be an indication of a trend reversal. However, the indicator can continue to go lower in a stair-step pattern. Since the indicator has a lookback period of a specific number of days, it can be somewhat lagging.