A pair of lines can fall into one of three categories when discussing 3-dimensional space:
• Intersecting: The two lines are coplanar (meaning that they lie on the same plane) and intersect at a single point.
• Parallel: The two lines are coplanar but never intersect because they travel through different points, while their direction vectors are scalar multiples of one another.
• Skew: The two lines are not coplanar but instead lie on parallel planes. This means they will never cross and do not have similar direction vectors. Because they lie on parallel planes, which share the same normal vector, the distance between the skew lines at their closest point can be calculated as the scalar projection of a vector pointing from one line to another onto the common normal vector.
