externality

(ĕkˌstər-nălˈĭ-tē)

1. The condition or quality of being external or externalized.
2. a. Something that is external.
   b. An incidental condition that may affect a course of action: “Our economic system treats environmental degradation as an externality—a cost that does not enter into the conventional arithmetic that determines how we use our resources” (Barry Commoner).