What is mantle made of?

I'm curious, could you elaborate on the composition of mantle? It's a term I've encountered frequently in various contexts, but its specific makeup remains a mystery to me. Is it a blend of multiple materials, or is it solely comprised of a singular substance? I'm eager to gain a deeper understanding of this elusive concept. Could you please shed some light on this matter? It would greatly assist me in piecing together the intricacies of this topic.