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 AB cuts a fixed curve BC, not in the same plane with straight line.
If AB is allowed to move so that it always remains parallel to its first position and always intersects the fixed curve BC, it will generate a curved surface, called cylindrical surface. The moving line is called the generator. the axis of the cylinder is the line joining the center of the bases. If O and O' are the centers of the top and the base then the line joining them is the axis of the cylinder. Cylinderical shapes objects occur very, in tanks and other containers, in pillers and in various parts of machines.
If the generating line is perpendicular to the base, then the cylinder is known as the right cylinder, otherwise oblique.