Once a bill is approved in Congress, the president has the option to sign it, veto it or make no action to acknowledge it. The president's signature is the final step to enact a law, but he must complete the process within 10 days, excluding Sundays. An official override, or veto, allows the president to reject a bill, sending it back to Congress for reconsideration.
A vetoed bill is returned to the Senate or House of Representatives, depending on which chamber it originated from. Congressional chambers have the power to override a presidential veto by holding an internal vote and obtaining a two-thirds majority. If the veto is overridden in one chamber, it must also be overturned with a two-thirds majority vote by members of the opposite chamber. As of 2014, only 109 vetoes have been overridden.
When the president takes no action on a bill, the unsigned legislation is enacted into law as long as Congress is still in session. If Congress has adjourned, and the 10-day grace period has passed, the bill is automatically overridden in a passive process known as a pocket veto. Past disputes about the conditions of adjournment have resulted in court rulings restricting the president to issuing pocket vetoes only when Congressional sessions are suspended without a specified future date. As of 2014, Franklin D. Roosevelt exercised his vetoing power more than any other president, overriding a total of 635 bills and facing only 9 Congressional overrides.