AutoCAD About Offsetting Objects
Using Offset Command
Creates a geometric object that is parallel or concentric to the selected object at a specified distance.
For example, if you offset a circle or an arc, a larger or smaller circle or arc is created, depending on which side you specify the offset. If you offset a poly-line, the result is a poly-line that parallels the original.
An effective drawing technique is to offset objects and then trim or extend their ends.
Use OFFSET to offset most of the geometric objects. Splines and polyline are trimmed automatically when the offset distance is larger than can otherwise be accommodated.