Final answer:
The President pro tempore is a Senate officer who presides over the Senate in the absence of the vice president and is third in presidential succession. They are traditionally the longest-serving senator of the majority party and are selected by Senate members.
Step-by-step explanation:
The Role and Selection of the President Pro Tempore
The President pro tempore of the United States Senate is an officer who presides over the Senate in the absence of the vice president. According to the U.S. Constitution, the vice president is the President of the Senate and only votes to break a tie. When the vice president is unavailable or is exercising the duties of the President of the United States, the President pro tempore steps in. This officer is also third in the line of succession for the presidency, following the Vice President and Speaker of the House. The Senate traditionally elects the President pro tempore from the ranks of the majority party's longest-serving member, which means this position is usually held by a senior senator.
The President pro tempore has both ceremonial and substantive roles. They partake in the proceedings of the Senate and fill the vice presidency in case there is a vacancy until a new vice president is confirmed by a majority vote of both Houses of Congress. Moreover, the President pro tempore may assume the duties of the lieutenant governor if there's a vacancy or inability to act.
The selection process is done by the members of the Senate, generally favoring a member with seniority from the majority party. This selection honors the service and commitment of long-standing members of the Senate, and it provides continuity and stability within the leadership of the Senate.