The model shows a right cylinder whose directrix is ​​a circle (cylinder of revolution, right circular cylinder). In addition to the directrix and a congruent circle, five generators are shown.

A cylinder is a ruled surface (a surface generated by straight lines) through an improper point (infinite point) and is defined by a guide curve. All generating lines of the surface thus meet the guide curve and are parallel to each other. The guide curve is usually chosen to be flat. A cylinder is called straight if its generating lines are normal to the supporting plane of the guide curve. Cylinders, along with cones and torsos, are developable surfaces. The surface is thus simply curved and generally consists exclusively of parabolic points.