Introduction to 3D Design - Autodesk AutoCAD 2013 Practical 3D Drafting and Design - page 24

Linear 3D entities
We can apply thickness to most linear 2D entities and also create linear 3D entities
like 3D polylines and splines.
Thickness
Almost all linear entities that we know from 2D have a property called Thickness,
whose value represents a height along the Z axis (a better word actually should be
height). This is the only 3D feature available in AutoCAD LT and can be applied to
text (if made with a text style that uses an SHX font), but beyond that is quite limited.
The best way to change the value of thickness is with the PROPERTIES command,
Ctrl + 1 . A line is still a line or a text still text, but with a proper visualization, these
entities can transmit a 3D feeling: