Those are your construction lines.
Be advised that this term is also used for 3D modeling, and you may need to filter CAD out of any web searches.
They can also be called guidelines.
When drawing figures, they're often called mannequins.
These terms can be a bit generic. What will help find tutorials or guides is a combination of
construction drawing + your art type, such as
You may find success looking at contour lines, as another answer suggests, but contour lines typically have a different connotation in drawing. Contours describe the visible surface and outlines. They don't describe the wireframe/unseen surfaces as seen in the tutorial you mentioned. Just be wary in looking for contour drawings, as that will lead you to a different type of exercise/drawing technique.