The presidents power to veto an act of congress is an example of

It is an example of checks and balances.

Explanation:

US constitution is unique because the three offices of American government have been given a certain constitutional powers to work distinctly without becoming authoritative.

Each branch of the government is stipulated with certain roles and responsibilities which cannot be overcome as each branch is authorized to exert supervisory and regulatory authority over the other so that no office becomes independent while exerting powers. Each office of the government is limited in their powers and all three offices are vested with equal powers