externality

1. The condition or quality of being external or externalized.
2. 1. Something that is external.
   2. 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).

A side-effect on others following from the actions of an individual or group. This effect is not bought by those affected and may be unwished for. Thus, while the acquisition of a car may benefit one household by improving mobility, it generates pollution and creates congestion for others.

Externalities may be positive—the building of a hall of residence may bring new business to a local shop—or negative—a new road scheme may create planning blight for home owners. Two types of externality are recognized: public behaviour externalities covering property, maintenance, crime, and public behaviour, and status externalities resulting from the social and ethnic standing of the household.

Side-effects, either harmful or beneficial, borne by those not directly involved in the production of a commodity.

The noun has one meaning:

Meaning #1: the quality or state of being outside or directed toward or relating to the outside or exterior
  Synonym: outwardness