In technical drawing, what term describes lightly drawn lines that are not part of the main sketch?

The term that describes lightly drawn lines that are not part of the main sketch is "Construction Lines." These lines serve as a guide in creating the main features of the drawing and are usually drawn faintly to avoid interfering with the visibility of the finished work. They help in laying out dimensions and proportions, allowing engineers and architects to visualize and position elements accurately before finalizing the design.

Construction lines can easily be erased or removed once the main elements of the drawing have been established, thus maintaining a clean and clear final presentation. Their role is crucial in both hand-drawn sketches and computer-aided designs (CAD), where precise alignment and proportions are essential for effective communication of ideas and designs.