The surface generated by a straight line intersecting and moving along a closed plane curve, the directrix, while remaining parallel to a fixed straight line that is not on or parallel to the plane of the directrix.

• 柱面一条直线与一个封闭的平面曲线相交及沿着平面曲线移动所形成的平面，准线则与一个不在此准线平面上或者不与此准线平面平行的固定直线保持平行