What is the term for lines that show structures or materials that are omitted from a drawing?

Phantom lines are used in technical drawings to represent elements that are not actually present in the physical space but are necessary to indicate for clarity. These lines often illustrate items such as future construction, alternate positions of a part, or existing features that are not directly associated with the current drawing context. They are typically depicted as long dashes alternating with short dashes, which helps differentiate them from other types of lines in a drawing.

In contrast, hidden lines indicate features that are not visible from the current viewpoint, such as edges or outlines behind other surfaces, and are typically represented by dashed lines. Center lines are used to denote the center of circular shapes or symmetry in drawings, shown as alternating long and short dashes, while construction lines are lightly drawn lines that serve as guides for measurements and layouts but do not represent any part of the finished work.