A hexahedron is a three-dimensional geometric shape that has six flat faces. The most common type of hexahedron is the cube, where all six faces are squares. Hexahedrons can also have faces that are rectangles or other shapes, but they always have six sides. In geometry, hexahedrons belong to a broader category called polyhedra, which are shapes with flat polygonal faces. Other examples of polyhedra include tetrahedrons and octahedrons. Hexahedrons are often studied in mathematics and are used in various fields, including architecture and computer graphics.