What is the 25x rule for retirement?

Could you please explain what the 25x rule for retirement entails? I'm curious to understand how this principle is applied and how it can help individuals plan for their retirement. Does it involve multiplying a certain factor by 25 to determine a target savings amount? If so, what is the basis for this multiplier, and how does it factor into retirement planning? Additionally, are there any assumptions or limitations to this rule that investors should be aware of?