What is the blur fee?

Excuse me, I've been hearing a lot about this concept called the "blur fee" in the cryptocurrency world, but I'm not entirely sure what it entails. Could you please explain in simple terms what a blur fee is? I understand it's related to transactions, but I'm not clear on how it works or why it's significant. Does it apply to all cryptocurrencies or just certain ones? Is it a fixed amount or does it vary based on transaction size? I'd appreciate any clarification you can provide on this matter.