Which term indicates that the music should return to the original tempo?

The term that indicates the music should return to the original tempo is often referred to as "A tempo." This directive instructs musicians to go back to the speed at which the piece started after a deviation, such as a slowing down or a change in pace during the performance.

Understanding this term is crucial in interpreting musical scores, as it helps performers maintain the intended flow and energy of the piece. Other terms like "rallentando" and "ritardando" are used to indicate a gradual slowing down of the tempo, which is the opposite of returning to the original speed. "Tempo primo," while also indicating a return to the original tempo, is less commonly used and can sometimes refer to the original tempo marking rather than a directive to perform.