Wikipedia
A fourrée is a coin, most often a counterfeit, that is made from a base metal core that has been plated with a precious metal to look like its solid metal counterpart. The term is normally applied to ancient silver-plated coins such as the Roman denarius and Greek drachma, but the term is also applied to other plated coins.
Cicero mentions that M. Marius Gratidianus, a praetor during the 80s BC, was widely praised for developing tests to detect false coins, and removing them from circulation. Gratidianus was killed under Sulla, who introduced his own anti-forgery law (lex Cornelia de falsis), that reintroduced serrated edges on precious metal coins, an anticounterfeiting measure that had been tried earlier.
Serrated denarii, or serrati, which featured about 20 notched chisel marks on the edge of the coin, were produced to demonstrate the integrity of the coin. This effort was in vain, as examples of fourrée serrati attest.