A sin tax is an excise tax specifically levied on certain goods and services deemed harmful to society and individuals. These goods and services include tobacco products, alcohol, drugs, candies, soft drinks, fast foods, coffee, sugar, gambling, and pornography. Sin taxes are used to increase the price of these goods and services in an effort to lower demand, or failing that, to increase and find new sources of revenue. They are different from Pigovian taxes, which are used to pay for the damage to society caused by these goods.

Sin taxes are usually placed on the sale of cigarettes, liquor, tobacco, and other goods that are considered dangerous to individuals or society. They are typically implemented to discourage consumption of the taxed products or to raise revenue for governments. Sin taxes are forms of excise or selective sales taxes. They are usually imposed as value-added taxes on various goods such as alcoholic drinks and cigarettes.

Proponents of sin taxes argue that the consumption of tobacco and alcohol, the behaviors associated with consumption, or both consumption and the behaviors of consumption, are immoral or "sinful", hence the label "sin tax". They believe that increasing taxes on these goods can help change behavior and improve health. Sin taxes also provide a source of revenue for governments.

Critics of sin tax argue that it is a regressive tax in nature and discriminates against the lower classes. Sin taxes are often assessed at a flat rate, meaning they account for a much larger portion of the price of a good or service by the wealthy. Additionally, sin taxes can result in the illegal manufacture, smuggling, and/or outright theft of the taxed products, sometimes for personal use but often for sale on the black market.

In conclusion, a sin tax is a tax levied on specific goods and services deemed harmful to society and individuals, such as tobacco, alcohol, drugs, candies, soft drinks, fast foods, coffee, sugar, gambling, and pornography. They are used to increase the price of these goods and services in an effort to lower demand or to raise revenue for governments. While proponents argue that sin taxes can help change behavior and improve health, critics argue that they are regressive in nature and can result in illegal activities.