A a solid figure on a flat surface is a plane figure (I do believe)
the flat surfaces of a solid figure are the
If you mean 1 flat surface and 1 vertex, then the only thing I can think of is a cone.
The flat surface of a solid figure is called a face. For example, a rectangular prism has 6 flat surfaces and therefore 6 faces.
A face is the flat surface on a solid figure. For example, a triangular prism has five flat surfaces and therefore five faces.
It is called a face.