A rectangular prism is a hexahedron with some rectangular sides. There is no requirement that all sides be rectangles. If they are, the solid is a right rectangular prism, or cuboid.
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A rectangular prism.
cuboid
A rectangular prism.
a cube
A hexahedron, or cube.
A cuboid.
Strictly speaking, any 3d figure with anything besides 6 sides cannot consist of rectangles. However, the name for an 8-sided figure is "octahedron".
A cube has six square faces. A cuboid also has six faces but 4 or 6 or them may be rectangles.
A butt
There is no form of a hexahedron whose name starts with a d.However, an octagonal prism has 6 (and more) faces, some of the are rectangles and it is a from of a decahedron.
It is a cuboid. It is a cuboid.