Square
It is a hexahedron, all of whose faces are rectangles.
A hexahedron with 8 vertices.
A Cylinder
It is a regular hexahedron - a prism with each side being a square.
Square
A hexahedron is a 3D shape with 6 faces. It CAN be a prism whose base is a square. But that is only one example. It can also be a prism whose base is any quadrilateral. It can also be something like a pentagonal pyramid (i.e. the base is a pentagon and the sides are made up of 5 triangles.)
It is a hexahedron, all of whose faces are rectangles.
It is a hexahedron, each of whose faces is a rectangle.
It can, but only if it a right triangular prism one of whose faces exactly matches the face of the square.
No, it is not.
An irregular hexahedron.
A hexahedron with 8 vertices.
A rectangular prism or a hexahedron.
A Cylinder
It is a regular hexahedron - a prism with each side being a square.
It is a rectangular prism or a right hexahedron.