Income tax, sometimes referred to as personal tax or direct tax, is an unavoidable obligation every individual has to fulfill. Although income tax is frequently used to refer to personal income tax, other synonyms can be used to represent a broader range of related terms. Some of these terms include progressive tax, levied on a sliding scale based on income, and flat tax, which charges all taxpayers an equal percentage of their income. Inheritance tax, gift tax, and estate tax are some synonyms that relate to income tax, but they are charged on different bases. Overall, these synonyms allow people to communicate about different types of taxes with varying policies, rules, and implications.