Because it is a solid figure which has six (prefix = hexa) faces.
A rectangular prism.
It is a cube
A polyhedron is a solid figure with many plane faces, usually greater than six. A polyhedron that has 7 faces is called a heptahedron.
There is no solid figure with only four edges. The smallest solid figure is the tetrahedron, made up of four triangular faces, but it has six edges.
Hexahedron
rectangular solid commonly called a box
Because it is a solid figure which has six (prefix = hexa) faces.
cubes and cuboids
A rectangular prism.
The solid shape/figure that has six rectangles as faces is called a rectangular prism. The general term for any shape with six faces, regardless of shape is a hexahedron.
A hexahedron is a solid with six plane faces, and a cuboid is a six-sided figure each face of which is a rectangle.
a cube
There is no such polyhedron.
It is a cube
A polyhedron is a solid figure with many plane faces, usually greater than six. A polyhedron that has 7 faces is called a heptahedron.
The general term is a hexahedron. If the six faces are all equal squares, then you can also call it a cube.