National Debt. The national debt is the amount of sums owing by a state to persons who have lent money to it, to enable it to carry on wars and other operations. A stipulated interest is paid to the national creditors or fundholders. The custom of borrowing money, and thus anticipating the available revenue for war purposes, was introduced in the reign of William III. Thus posterity is taxed, for wars of which perhaps it will disapprove. The total amount of the national debt of Great Britain is now upwards of eight hundred millions.