This .NET class wraps the AcDbRegion ObjectARX class. 

Objects of this class represent region entities in AutoCAD. 

An Region entity is a container and interface for a ShapeManager object that is the actual geometrical representation of the region. This class provides no provisions for directly manipulating the edges, vertices, or faces of the ShapeManager object that is the actual region representation.

Autodesk.AutoCAD.DatabaseServices.DBObject
    Autodesk.AutoCAD.DatabaseServices.Entity
        Autodesk.AutoCAD.DatabaseServices.Region

Public Class Region
Inherits Entity

public class Region : Entity;