The rotating body surrounded by the straight line where one side of the rectangle is located is called a cylinder, that is, one side of the rectangle AG is the axis, and the geometry obtained by rotating 360 degrees is a cylinder. Among them, AG is called the axis of the cylinder, the length of AG is called the height of the cylinder, all the line segments parallel to AG are called the generatrix of the cylinder, the two circles formed by the rotation of DA and D'G are called the bottom surface of the cylinder, and the surface formed by the rotation of D' D is called the curved surface.