Clubul Sportiv Orășenesc Plopeni, commonly known as CSO Plopeni, or simply as Plopeni, is a Romanian amateur football club based in Plopeni, Prahova County. The club was originally established in 1947 under the name of Metalul Plopeni.

The Liga 3, most often spelled as Liga III, is the third level of the Romanian football league system. It was founded in 1936 and was called Divizia C until 2006. An exception was the seasons 1992–93 to 1996–97, in which the league was called Divizia B. Its name was changed from Divizia C to Liga III before the start of the 2006–07 season.