Cambridge Definition
to reduce a company's borrowing in relation to its share capital
Wikipedia Definition
At the macro-economic level, deleveraging of an economy refers to the simultaneous reduction of debt levels in multiple sectors, including private sectors and the government sector. It is usually measured as a decline of the total debt to GDP ratio in the national accounts. The deleveraging of an economy following a financial crisis has significant macro-economic consequences and is often associated with severe recessions.