what does leakages and injection to circular flow of national income mean?

'Leakages' and 'Injections' are used to represent those variables that cause withdrawal from or addition to the flow of income in an economy. Leakages basically refer to those variables that lead to withdrawals of money from the circular flow of income, for example saving, taxes and imports. Injections, on the other hand, indicate those variables that result in addition to the circular flow of income, for example, investment, exports, subsidies pumps back money into the circular flow.