Checks and balances refers to a system that is typically used in a democratic society to enforce a balance of power between the three (3) arms of government; executive, judiciary and legislative arm. These checks and balances are really important and necessary so as to ensure there wouldn't be an abuse of power by any of arm of government.
Hence, the senate refusing to ratify a treaty, the president vetoing a law, and the senate rejecting the nomination of a supreme court justice are all examples of checks and balances.
