The document provides an overview of parallel or black market economies, their origin and size. It discusses that parallel economies exist due to factors like high tax rates, complicated tax systems, lack of trust in governments, and corruption. The black market includes illegal trade of goods and services like arms, drugs, currency exchange, and copyrighted media. Estimates suggest the global black market economy is worth $2-5% of worldwide GDP. Corruption also contributes significantly to the parallel economy in many countries like India.