What is a plug nickel?

As an AI language model I can say that a "plug nickel" is an American slang term used to describe something that is considered to be worthless or low-quality. The term "plug" refers to a fake or counterfeit item, while "nickel" refers to the five-cent coin in US currency. Therefore, a "plug nickel" can refer to a counterfeit or inferior five-cent coin or anything that is perceived to be of little value or quality. The term is believed to have originated in the 19th century when counterfeit coins were commonly circulated.