A business is defined to include every trade, manufacture, adventure in the nature trade. Business income is subject to tax. Sec 3(2) a i

Businesses are taxed on their profits. Taxable profits differ from accounting profits.  Profit is the excess of incomes over expenses. However for purposes of  ascertaining the  taxable profits, distinction has to be made between taxable incomes and non taxable income and between allowable expenses and disallowable expenses.