The answer is - a cone.
If you have one flat face and I have one curved face, which one of us is the 3d shape? Anyway, a 3d shape with pne f;at, circular face and one curved face could be: a section of a sphere or a section of an ellipsoid cut by a plane parallel to one of its axes, a section of a paraboloid or a cone. There are probably other shapes.
A cone would fit the given description
It could be a semi-sphere but mostly it's a cone.