The president of the United States is the head of the executive branch and plays a large role in making America's laws. His job is to approve the laws that Congress creates. When both chambers have approved a bill, they send it to the president. In order for the bill to become law, the president must sign it into law. The president can decide not to sign a bill if he does not want it to become law.

What is it called when the president refuses to sign a bill into law?