What is the 3 rule in retirement?

Excuse me, could you elaborate on what you mean by "the 3 rule in retirement"? Is it a specific financial strategy or a guideline that retirees often follow? I'm interested in understanding the concept behind it, as it could potentially be a useful tool for individuals planning for their retirement. Could you please provide a concise explanation of what the 3 rule entails and how it can benefit those who are approaching or already in retirement?