Thin lines that serve as guides while sketching or drawing?

Thin lines that serve as guides while sketching or drawing are often referred to as construction lines or guidelines. These lines are typically light and non-permanent, used to establish proportions, perspectives, and the overall composition of the artwork. They help artists maintain accuracy and symmetry before finalizing their drawings with darker, more defined lines. Once the drawing is complete, these construction lines can be erased or left faint to avoid distracting from the final piece.