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In the United States, the office of lieutenant governor is the second-highest executive office in a state and is nominally subordinate to the governor. In the U.S., the main duty of the lieutenant governor is to act as governor should the governor be temporarily absent from the office. In addition, the lieutenant governor generally succeeds a governor who dies, resigns or is removed in trial by the legislative branch. In most states, the lieutenant governor then becomes governor, with the title and its associated salary, office, and privileges. In a few states, like Massachusetts, the lieutenant governor instead becomes "acting governor" until the next election.
Other than this primary constitutional duty, most state constitutions do not prescribe the duties of the lieutenant governor in detail.
https://ballotpedia.org/Lieutenant_Governor_(state_executive_office)