What are three facts about the mantle?

I'm curious to learn more about the mantle. Could you please enlighten me with three key facts about it? First off, what exactly does the mantle refer to in the context we're discussing? Secondly, could you elaborate on its significance or role? And finally, are there any particular characteristics or attributes associated with the mantle that are worth noting? I'm particularly interested in understanding its essence and how it fits into the broader picture. Thank you in advance for sharing your insights.