Some curved surfaces may be defined as generated by straight lines which are thought of as moving and changing its direction continuously. Suppose that the line cuts a fixed curve , not in the same plane with straight line.
If is allowed to move so that it always remains parallel to its first position and always intersects the fixed curve , it will generate a curved surface, called cylindrical surface.
A cylinder is a solid figure generated by a straight line moving to its original position, while its end describes a closed figure in a plane. It is thus a limiting case of a prism whole ends would be circles, ellipse and parabola etc.
If the generating line is perpendicular to the base, then the cylinder is known as the right cylinder, otherwise oblique.