An economic side effect or consequence that affects an uninvolved third party; it can be either positive or negative. Pollution is a common negative externality that affects the environment and public health.
A factor or element that is not considered in a decision-making process but has an impact on the outcome. The company failed to account for the externality of increased traffic congestion when planning their new headquarters.
The quality or state of being external; exteriority. Philosophers have long debated the externality of the physical world in relation to consciousness.