The term "underground economy" can be referred to using a number of different synonyms that reflect the various aspects of this economic phenomenon. The "black market" suggests illegal trade in goods and services, while "shadow economy" refers to hidden economic activity that evades taxation and regulation. Other terms include "informal economy" which encompasses unregulated economic activity and "grey economy" which involves legal but unreported income. "Parallel economy" describes activities that are disguised as legitimate businesses. A "subterranean economy" suggests hidden and secretive economic activity, and "clandestine economy" refers to economic transactions that occur without the knowledge of authorities or the public. Regardless of the term used, these synonyms all describe economic activity that takes place outside of the traditional, visible economy and often exploits legal loopholes or social vulnerabilities.