What term would instruct the musician to play louder than piano but softer than mezzo forte?

The term that instructs the musician to play louder than piano but softer than mezzo forte is "mezzo piano." This indicates a dynamic level that is moderately soft. In musical terminology, "piano" refers to playing softly, while "mezzo forte" indicates a moderately loud dynamic. The term "mezzo piano" serves as a bridge between these two dynamics, providing a clear instruction for the performer to maintain a sound level that is in the middle of the soft and moderately loud spectrum. This nuanced level is important for conveying the appropriate expression and dynamics within a piece of music.

Other terms listed do not fit in this context: "pianissimo" indicates a very soft dynamic, while "presto" refers to a very fast tempo and is unrelated to dynamics.