Its surface, would you believe!
Each surface of a polyhedron is called a face.
It is a face of the polyhedron
It is called the surface area.
Face
They are its faces
In normal usage "polyhedron" refers to solids whose edges are straight lines, not curves, so a strict answer would be: there is no such polyhedron.
It is called a face of the polyhedron.
A polyhedron is a solid object bounded by polygons. Polygons are plane shapes [bounded by straight lines]. The curved surface of a cone is not a polygon and so the cone is not bounded by polygons and therefore, a cone is not a polyhedron.
Because that is how a polyhedron is defined.
Because that is how a polyhedron is defined.
a base
They are the faces of the polyhedron.