| Term | Definition |
| Object Line | A heavy solid line used on a drawing to represent the outline of an object. |
| Hidden Line | A line type that represents an edge that is not directly visible, because it is behind or beneath another surface. |
| Center Line | A line consisting of a long dash followed by a short dash that is used to show and locate centers of arcs and cricles, and to describe the center axis of cylindrical forms |
| Phantom Line | A line used to show the alternate positions of an object or matching part without interfering with the main drawing. |