When a musician sees "A tempo" in the music, what action should they take?

When a musician sees "A tempo" in the music, they should return to the original tempo of the piece. This term indicates that the performer should revert to the speed that was established earlier in the composition after having played at a different tempo, which may have been indicated by a previous instruction.

The context for this term typically arises after a section of music that may have called for a change in tempo, such as "Accelerando" (speeding up) or "Ritardando" (slowing down). Therefore, "A tempo" acts as a directive to recover and adhere to the composition's initial pacing, ensuring that the overall musical structure and flow are maintained as intended by the composer.