Going by the simplest possible definition of presidential veto, it is the power given to the executive head of the state―the President―to prohibit or reject a proposed or intended piece of legislation. (The term 'veto' is basically a Latin word for 'I forbid'.) While that gives the reader a rough idea about its use in democracy, there is much more to know about it, including the procedure that should be followed, how it can be overridden, what margin is required to override it, etc. What is a Presidential Veto? The presidential veto is the first and one of the most important legislative powers given to the President of the United States. As per the Presentment Clause of the U.S. Constitution, any legislation that has been passed by both houses of the United States Congress has to be presented before the U.S. President for his/her approval before it can go on to become a law. The President can either sign the same―in which case it becomes a law, take no action on it―in which case it becomes an unsigned law, or raise objection and return it to the Congress along with the suggested changes. If the President returns the legislation to the Congress with an explanation on why he/she vetoed it, it is referred to as a regular veto, which is one of the two types of presidential vetoes. In the second type, which is referred to as 'pocket veto', the President indirectly vetoes the legislation by refusing to sign it and therefore, the legislation fails to become a law. This is basically the case when the Congress adjourns during the period of 10 days, which is given to the President to sign or veto the legislation. How Can Congress Override it? A veto override is the action taken by the legislature to pass a bill overriding the executive head's veto. This power of overriding a veto tends to differ from one nation to another. In the United States, 2/3 majority in both the Houses of the Congress, is the margin that is required to override a presidential veto. In other words, the U.S. Congress can override the President's veto if there is a majority of 2/3 in both, the House of Representatives and Senate. In this manner, the legislation is enacted into a law even after it is vetoed by the President. That, however, only works in case of a regular veto, and not a pocket veto. The latter cannot be overridden as Congress cannot vote while in adjournment. Most of the states in the U.S. also have similar regulations about veto overriding. In 1812, James Madison became the first President to use the power of pocket veto. There have been 2563 instances of vetoing in American history, of which 1496 were regular vetoes and 1067 were pocket vetoes. Of these, the number of vetoes overridden by Congress stands at 110, which roughly amounts to 4 percent of the total. Some of the most famous presidential vetoes include Andrew Jackson's vetoing of the Second Bank of the United States Re-Charter in 1832, Abraham Lincoln's pocket vetoing of Wade-Davis bill in 1964, Bill Clinton's pocket vetoing of Bankruptcy Reform Act of 2000, and Barack Obama's vetoing of the Interstate Recognition of Notarizations Act.