The parallel economy refers to economic activities that are unreported or unmeasured by a country's methods for tracking its economy. It includes both legal and illegal activities. The parallel economy exists due to factors like high tax rates, complex tax systems, corruption, and lack of trust in the government. It encompasses black markets for goods like arms, drugs, and copyrighted media. Estimates suggest the parallel economy makes up 2-5% of global GDP. Measuring its full size is difficult due to its covert nature. Reducing tax evasion, implementing disclosure programs, and reforming the currency system could help address the parallel economy.