Under Article I, Section 7 of the United States Constitution, the president has the authority to veto legislation that is passed by Congress. After receiving a legislative bill, the president is given 10 days to sign the bill into law or to veto it, either by regular or pocket veto.
A regular veto occurs when the president returns the unsigned bill to the House or Senate within 10 days of receiving it. Usually, the president will include a veto message explaining his decision to veto the bill. If Congress chooses, it can override the decision, provided it can get 2/3 of the members of both houses to approve.
By contrast, a pocket veto occurs when Congress has adjourned and the president fails to sign the bill. Because Congress is not in session to muster approval to override the veto, it is an absolute veto and has become a historical source of debate in the courts.
Notably, the power of veto has been employed 2,563 times in U.S. history. President Franklin D. Roosevelt used the power of veto the most, with 372 regular and 263 pocket vetoes to his credit. Congress overrode only nine of those vetoes. Historically, Congress has overridden just 109 vetoes, as of 2014.