There are three types of are vetoes exercised in U.S. government: the regular veto, the pocket veto and the line item veto. The U.S. Constitution grants the president the authority to use the regular and pocket vetoes.
A regular veto involves the president returning legislation to the originating chamber of Congress unsigned within 10 days of having received it. Congress can override this type of veto with a two-thirds vote of both of its houses.
A pocket veto cannot be overridden. It takes place when Congress adjourns during the 10-day period during which the President can return a bill unsigned. By simply not signing the legislation, the pocket veto takes effect.
A line item veto involves vetoing selected items of a piece of legislation while approving the remainder. The U.S. President does not have this authority, but some state constitutions give it to their governors.