Which of the following is not a type of unemployment?

Cyclical unemployment refers to the fluctuations in the economy that lead to job loss during periods of economic downturns. Structural unemployment occurs when there is a mismatch between workers' skills and job requirements, often due to technological changes or shifts in the economy. Frictional unemployment includes the time it takes for workers to transition between jobs or enter the workforce.

Environmental unemployment is not recognized as a formal category of unemployment within economic theory. While environmental factors may influence employment or specific industries, this term does not have a standard definition in the context of unemployment measurement and analysis. Thus, identifying it as a non-type of unemployment is correct.