In Australia, a taxpayer's income is taxed progressively. Broadly, this means that as you earn more income your average tax rate rises. Progressive taxation means that higher income earners pay more tax than lower income earners. This is achieved by taxing a range of income brackets as a set percentage or cents in the dollar. These income brackets are called tax brackets. The rate of tax within these brackets is called the marginal rate of tax. Tax is applied to every dollar after this figure. This tax-free amount is called the tax-free threshold.
For more information about Sole Trader Income Tax please see the Tax Pack information at the ATO website.