A veto override occurs when a legislative body, typically the Congress, votes to pass a bill despite a veto by the executive branch, usually the president. In the U.S., this requires a two-thirds majority vote in both chambers of Congress. Veto overrides reflect the legislative branch's power to check the executive's authority, allowing it to enact laws even in the face of opposition from the president. This mechanism is crucial for maintaining balance in governance and ensuring that elected representatives can fulfill their legislative mandates.