A presidential veto is the constitutional power granted to the President to reject legislation passed by Congress. When a bill is vetoed, it does not become law unless Congress overrides the veto with a two-thirds majority vote in both chambers. This mechanism serves as a check on congressional power, allowing the President to influence legislative outcomes. Vetoes can be strategic tools for shaping policy direction and signaling priorities, serving as a powerful expression of the executive's authority within the system of checks and balances.