noun.
The state of being external or externalized.
noun.
A thing that is external relative to something else.
noun.
An impact, positive or negative, on any party not involved in a given economic transaction or act.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
the quality or state of being outside or directed toward or relating to the outside or exterior
Word Usage
"In this case, the externality is the relationship with the neighbours, especially since those who would be most disappointed are also likely to be the most active in the community."