Walk forward is a sliding windows validation process which cuts your backtesting period into smaller In Sample and Out of Sample period say theres 12 weeks of your data cut it into 4 weeks of in sample and 2 weeks of out of sample and reoptimize every OOS period. WFO 1 IS : 1- 4 Optimize OOS : 5 -6 WFO 2 3- 6 Optimize OOS : 7 - 8 And Etc Calculate the total OOS net profit, and should give you a more realistic view of your system performance during live trading since you are most likely to try to reoptimize your system during live trading like what the WFO does.