Tax Base/Broad Tax Base

The total amount of income, wealth, or spending that a tax system covers.
A broad tax base means fewer loopholes and less opportunity for avoidance.
Aotearoa has a broad base for income and consumer spending (personal and company income tax and GST) except that it largely misses income from capital gains—but a narrow base for wealth, which is why the system is unbalanced.
Visual idea: A net catching fish: wide net vs full of holes.