Arthur Pigou gave his name to a tax on activities that create harmful side effects, such as pollution.
A Pigouvian tax is intended to make the private cost of an activity reflect its wider social cost. If a factory pollutes a river, for example, the factory may pay only for its own production while nearby communities bear health or environmental costs. A tax linked to that harm can encourage producers and consumers to reduce it.
Pigou developed this idea in The Economics of Welfare, first published in 1920. His work helped establish the economic study of externalities, meaning costs or benefits affecting people who are not directly involved in a transaction.
A Pigouvian tax is not simply any tax on an unpopular product. Its defining purpose is to correct an externality. Carbon taxes and congestion charges are often discussed as modern examples, although their real-world design may also pursue revenue or policy goals.