If the instance is contained within another element, this property returns the containing element. An instance that is face hosted will return the element containing the face.
Assembly: RevitAPI (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0)
An example of an instance that is contained is a window. In this case the host property would return the wall in which the window is contained. Another example is an instance that is hosted to a planar or curved face in a Mass element will return the Mass element.