What do you call 'perpendicular but skew' lines?

Question

For example, the seat tube and rear axle of a bicycle or motorcycle. That is, when viewed from above, the seat tube would appear 'perpendicular' to the rear axle. But in 3d reality, the lines are skew. I was wondering if there is a single word or concise way to describe such lines.

Answer 1

Let $m$ and $n$ be "perpendicular but skew" lines. I suppose that you need to introduce a line parallel to $m$, call it $m_1$, such that $m_1$ and $n$ are coplanar. If $m_1$ and $n$ are coplanar they can be perpendicular to each other. So, now we have $n \perp m_1$.

So essentially $m$ is parallel to a line which is perpendicular to $n$. $m_1$ is coplanar to both $m$ and $n$. I think that Najib Idrissi's comment about orthogonal projections might help you explain the relationship by noting that if you project $m$ into a plane containing $n$ you will find $m$'s projection to be perpendicular.

EDIT: updated summary of Najib's comment.