It is a definitional requirement. If any face is not flat, then it is not a polyhedron.
Yes
A polyhedron.
They are the faces of the polyhedron.
A cube is a solid figure called a polyhedron. A polyhedron is a solid figure with all flat faces. So a cone would be a solid figure but not a polyhedron becasue it has a curve and does not have all flat faces.
Yes and its flat surface faces are in regular shapes.
A sphere is not a polyhedron because it has no edges, no vertices and no flat faces The word 'polyhedron' means many faces.
faces
They are its faces
a 3d object made of 2d faces with all flat sides
a polyhedron
A polyhedron
A polyhedron.