| 
 | 
 | 
A Ruled Surface is called a generalized cylinder if it can be parameterized by 
,
where 
 is a fixed point.  A generalized cylinder is a Regular Surface wherever 
.  The above surface is a generalized cylinder over a Cardioid.  A generalized cylinder is a 
Flat Surface.
See also Cylinder
References
Gray, A.  Modern Differential Geometry of Curves and Surfaces.  Boca Raton, FL: CRC Press, pp. 341-342, 1993.