Basic rate
From ACT Wiki
1. Tax - Income Tax.
A basic rate of income tax is the rate most commonly paid by the largest number of taxpayers on the largest proportion of their taxable income.
The charging of higher rates on higher levels of taxable income is generally part of a tax regime designed to be progressive.
2. Other measures and calculations.
In other contexts, any default amount of money - or other amount or proportion - used for calculation of a standard entitlement or measure.