Line Categories in ARCHICAD

Drafting line: Simple 2D drafting line. Lines drawn with the Line tool will be in this category by default.
Cut line: Contour line of a 3D element on a cutting plane.
Note: You can choose to display lines in the Cut line category in boldface: In View > On-Screen View Options, choose Bold Cut Lines.
Skin Separator Line: Separator line between skins of composite structures, including walls, columns, slabs and roofs.