异面直线skew line
专业英文释义：
In geometry, two lines are said to be skew lines if they do not intersect but are not parallel.
Skew lines only exist in three or more dimensions; any two lines in the plane which are not parallel must intersect at some point. In fact, two lines are skew lines if and only if they do not lie in a single plane together. This means that if each line is defined by two points, these four points must not be coplanar; put another way, they must be the vertices of a tetrahedron of nonzero volume. Any three of them will still be coplanar, since three points define a plane, but no three points will be collinear, since this would make all four points coplanar.