To tax is to impose a financial charge or other levy upon a taxpayer (an individual or legal entity) by a state or the functional equivalent of a state such that failure to pay is punishable by law. Taxes are also imposed by many subnational entities. Taxes consist of direct tax or indirect tax, and may be paid in money or as its labour equivalent (often but not always unpaid). A tax may be defined as a "pecuniary burden laid upon individuals or property to support the government,  a payment exacted by legislative authority." A tax "is not a voluntary payment or donation, but an enforced contribution, exacted pursuant to legislative authority" and is "any contribution imposed by government [whether under the name of toll, tribute, tallage, gabel, impost, duty, custom, excise, subsidy, aid, supply, or other name."
The Four "R"s
Taxation has four main purposes or effects: Revenue, Redistribution, Repricing, and Representation. The main purpose is revenue: taxes raise money to spend on roads, schools and hospitals, and on more indirect government functions like market regulation or legal systems. This is the most widely known function. A second is redistribution. Normally, this means transferring wealth from the richer sections of society to poorer sections. A third purpose of taxation is repricing. Taxes are levied to address externalities: tobacco is taxed, for example, to discourage smoking, and many people advocate policies such as implementing a carbon tax. A fourth, consequential effect of taxation in its historical setting has been representation. 

Tax rate
Taxes are most often levied as a percentage, called the tax rate. An important distinction when talking about tax rates is to distinguish between the marginal rate and the effective (average) rate. The effective rate is the total tax paid divided by the total amount the tax is paid on, while the marginal rate is the rate paid on the next dollar of income earned. For example, if income is taxed on a formula of 5% from $0 up to $50,000, 10% from $50,000 to $100,000, and 15% over $100,000, a taxpayer with income of $175,000 would pay a total of $18,750 in taxes. /wikipedia.org/

deduction -  вычет, налоговая льгота

standard deduction - стандартный вычет из облагаемого дохода

ad valorem - налог на стоимость

inheritance tax - налог на наследство

exemption - освобождение от уплаты налога

business tax - налог на предпринимательскую деятельность

poll tax - подушный налог с избирателей

taxable income - налогооблагаемый доход

capital gains tax - налог на увеличение рыночной стоимости капитала

property tax - поимущественный налог

voluntary - добровольный

consumption tax - налог на потребление

retirement tax - налоговые поступления для погашения государственного долга

withhold - удерживать, вычитать

corporate tax - налог с доходов корпорации

sales tax - налог с оборота

credits - льготы, скидки

excess profits tax, Windfall profits tax - налог на сверхприбыль

tariff - тариф

taxpayer - налогоплательщик

environment affecting tax - налог за загрязнение окружающей среды

toll - пошлина, сбор

pecuniary - денежный, финансовый

excise - акциз, акцизный сбор

transfer tax - налог на денежные переводы за границу

tallage - налоги, сборы

income tax - подоходный налог

value added tax - налог на добавленную стоимость

impost - налог, пошлина

marginal tax rate - предельная налоговая ставка

effective (average) rate - фактическая налоговая ставка