A system is defined as a set of rules which you follow in trading. It essentially has below components: Instrument : The instrument such as Stock, Futures or Options Entry criterion : When are you going to take a Sell/Buy position in the instrument. It can be time based such as 0930 AM or it can be based on indicator e.g. if an instrument/stock price moves above 50 day moving average etc. Exit Criterion : When are you going to exit the position. Exit can be based on a stop loss, a target or a particular time e.g. in intraday systems positions need to be exited before market close Power of large numbers : All systems are based on belief that if you keep doing same thing again and again then you will make money in long term. Here back testing is of good use where once a system is formed it can be back tested to see if it is profitable in past. Though this doesn't guarantee that system will perform well in future but probability of it being profitable in future will be high. Strategi