In terms of tempo, what does "tempo primo" refer to?

"Tempo primo" refers specifically to a return to the original tempo or the initial speed at which a piece of music was played. This term is used in musical notation to indicate that after a section that may have altered the tempo (either speeding up or slowing down), the performer should revert back to the original speed established at the beginning of the piece. It serves as a guiding instruction for musicians to maintain structural coherence throughout the performance.

In this context, the other options do not pertain to the definition of "tempo primo." A very soft dynamic pertains to volume rather than speed, a gradually increasing tempo relates to a different kind of alteration (accelerando), and extremely fast speed does not align with the concept of returning to a previously identified tempo. Thus, understanding these concepts in musical dynamics and tempo enhances a musician's ability to interpret scores accurately while performing.