In the USA:

What Does Veto Mean?

The word “veto” means “I forbid” in Latin. In the United States, Article I, Section 7 of the Constitution gives the president the authority to reject legislation that has been passed by both houses of Congress, though the word “veto” doesn’t actually appear in the Constitution.

Congress can override a presidential veto with a two-thirds majority vote in both the House of Representatives and the Senate, but this is very difficult to achieve. Even the threat of a veto allows the president to influence debate on legislation in Congress before a bill is passed, and pressure legislators to make changes to a bill to avoid the veto.

Both the veto power and Congress’ ability to override it are examples of the system of checks and balances the Constitution created to ensure the separation of powers and keep any one branch of government from becoming too powerful.