The given problem involves understanding a specific macroeconomic relationship concerning GDP and unemployment. To identify the correct term for this relationship:
1. The problem describes a scenario where the difference between actual GDP and trend output varies inversely with the difference between the actual unemployment rate and the natural rate of unemployment.
2. This inverse relationship is known in macroeconomics as Okun's Law. It indicates that higher unemployment typically correlates with a GDP that is below potential output, reflecting economic inefficiencies.
3. Okun's Law is a well-established empirical relationship suggesting that effective economic policies must consider the trade-off between GDP growth and unemployment.
Other options like the New Keynesian aggregate supply curve, Taylor Rule, and New Keynesian Phillips curve focus on different macroeconomic concepts:
Therefore, the correct answer is Okun's law.