平行线，平行面如直线或平面等一组平行的几何图形之一
One of a set of parallel geometric figures, such as lines or planes.
母点，母线形成一个几何图形的几何要素，尤指通过以规定方式运动而产生一个面的一条直线
A geometric element that generates a geometric figure, especially a straight line that generates a surface by moving in a specified fashion.
射影的指定几何图形属性的，以便当这个图形经受影射时不发生变化
Designating a property of a geometric figure that does not vary when the figure undergoes projection.
