The thing or amount to which a tax rate applies. To collect income tax, for example, you need a meaningful definition of income. Definitions of the tax base can vary enormously, over time and among countries, especially when tax breaks are taken into account. As a result, a country with a comparatively high tax rate may not have a high tax burden if it has a more narrowly defined tax base than other countries. In recent years, the political unpopularity of high tax rates has lead many governments to lower rates and at the same time broaden the tax base, often leaving the tax burden unchanged.