Step 1: Recall government functions.
- Allocative Function: Proper allocation of resources between private and public goods.
- Distribution Function: Redistribution of income and wealth through taxes and subsidies.
- Stabilization Function: Government intervention to maintain stability in prices, output, and employment.
- Fiscal Function: General role of government in taxation and expenditure.
Step 2: Apply to the question.
The question mentions “expand or reduce demand”, which directly refers to stabilization policies (using fiscal/monetary measures to control aggregate demand).
Final Answer:
\[
\boxed{\text{Stabilization Function}}
\]