A slug is a counterfeit coin that is illegally used to make purchases. The object substituted may be an inexpensive object such as a washer or a coin from another country with far lower purchasing power than the coin it is being passed off as.
While slugs are sometimes passed off to cashiers and other unwitting human recipients, they are more commonly used in automated coin-operated devices such as a vending machine, payphone, parking meter, transit farebox, copy machine, coin laundry, gaming machine, or arcade game.[1] By resembling various features of a genuine coin, including the weight, size, and shape, and/or by mixing it with genuine coinage a slug is intended to trick the recipient into accepting it as a real coin.
Losses caused to vendors by slug usage may be the result of the loss of sales revenue following the distribution of merchandise that was obtained at the vendor's expense as well as the loss of cash that is distributed by the machine for overpayment with slugs. Honest customers may also suffer losses when change returned for overpayment is in the form of a slug rather than a genuine coin. Customer losses may be either unintentional on the part of merchants (such as when perpetrated by unwitting cashiers or machines designed to automatically process previous payments as change for later customers) or the result of the deliberate substitution of genuine coinage by corrupt cashiers and vending machine operators.
Though slug usage is illegal in the United States and elsewhere,[2] prosecution for slug usage is rare due to the low value of each theft, the difficulty in identifying an offender, and also the difficulty in proving mens rea (especially when the slug is another country's genuine coin) since perpetrators when confronted will often claim the substitution was an "honest" mistake. Offenders in casinos are most likely to be prosecuted, as casinos have high levels of video surveillance and other security measures, and tend to be more proactive in enforcement.