Generally, it includes some or all items of income and is reduced by expenses and other deductions.[2] The amounts included as income, expenses, and other deductions vary by country or system. Many systems provide that some types of income are not taxable (sometimes called non-assessable income) and some expenditures not deductible in computing taxable income.[3] Some systems base tax on taxable income of the current period, and some on prior periods. Taxable income may refer to the income of any taxpayer, including individuals and corporations, as well as entities that themselves do not pay tax, such as partnerships, in which case it may be called “net profit”.