Institutional arrangements that let each branch or level of government limit the others, so that no single body can exercise power unchecked.
In more detail
Unlike a strict separation of powers, checks and balances give branches overlapping powers, for example a veto, impeachment, judicial review or bicameral approval, so that they can resist each other. In Federalist 51 Madison argued that ambition must be made to counteract ambition. Critics note that dense checks can produce gridlock and blur responsibility, since many actors share a decision.