What is Deep Backtesting?
Deep Backtesting is an additional mode of operation of the Strategy Tester, which makes it possible to calculate the strategy on all historical data available for the selected symbol, and not only on those loaded on the chart.
The main difference between Deep Backtesting and the regular Strategy Tester backtesting is the ability to select a specific date range for strategy calculation. How it works can be found here.
Please note that the calculation results in the regular Strategy Tester backtesting and in the Deep Backtesting mode may differ. This is further explained here.