Definition - What does Veto mean?
A veto is the right of an official to reject a bill or another piece of legislation that is presented for signature. Only certain officials have this power. For example, the President of the United States can veto bills presented by Congress. In the context of the law, a bill will not be automatically accepted as law if the President vetoes it. Instead, it will be sent back to Congress.
Justipedia explains Veto
Veto power is highly significant in American law because it can literally determine whether or not a bill becomes a law and goes into effect. Congress can still pass a law if the President issues a veto on a bill. However, the bill would then have to get two-thirds majority approval from both houses of Congress. State governments commonly give governors the same veto power that the president has, at the state level.