What is the 3-5-7 rule in trading?

Could you please explain what the 3-5-7 rule stands for in the context of trading? I've heard it mentioned a few times but haven't quite grasped its significance. Is it a risk management technique, or does it relate to market timing? Also, could you provide some examples or scenarios where this rule might be applied? It would be helpful to understand how it fits into a trader's overall strategy.