Underground markets, also known as shadow markets, black markets, or clandestine markets, are illegal and unregulated marketplaces that operate outside the purview of government regulations. These markets can sell illegal goods and services like drugs, counterfeit products, and prostitution. Other synonyms for underground markets include grey markets, where goods or services are sold outside of authorized distribution channels. Parallel markets are another term that describes the illegal market activity. They can also be called informal markets and typically operate in low-income areas, selling goods and services that are in demand but may not meet legal standards. Regardless of the synonym, all underground markets operate in secrecy and without the proper oversight that protects consumers.