Answer: Externalities occur when the actions of an individual or group spill over onto others, without their consent.
Step-by-step explanation:
By definition, an Externality is the effect of an action by an individual or group that spills over onto third parties without their consent.
Externalities can be either negative or positive. A positive externality for instance would be bees from a bee farm pollinating flowers in the environment.
A negative externality would be air pollution from China for instance contributing to global warming effects experienced in Northern Africa.