What is the 15 minute rule in trading?

I'm curious, what exactly is the 15 minute rule in trading? I've heard it mentioned a few times but haven't quite grasped its significance. Is it a common strategy that traders use to make decisions or is it more of a guideline? Can you explain the concept and its potential applications in a trading context? Also, are there any specific market conditions or asset types where this rule is particularly effective? I'd appreciate your insights on this matter.