Hexagonal Close Packing (HCP) is a method of arranging spheres in a three-dimensional space to achieve maximum density. In this structure, each sphere is surrounded by twelve others, forming a hexagonal pattern in each layer. The layers are stacked in an alternating manner, which helps to minimize empty space and maximize the number of spheres that can fit together. This packing arrangement is commonly found in metals like magnesium and titanium, where atoms are closely packed to enhance stability and strength. HCP is one of the most efficient ways to pack spheres, alongside cubic close packing (CCP), which also achieves high density.