What is the mantle and why is it important?

Could you kindly explain, in plain English, what exactly the mantle refers to? And why does it carry such significant importance? I've heard it mentioned in several contexts related to finance and cryptocurrencies, but I'm still unclear about its exact meaning and the reasons behind its significance. Could you elaborate on this concept, perhaps with some examples or use cases? I'm eager to gain a deeper understanding of this topic and appreciate your assistance in clarifying it.