Which term is used to instruct musicians to play at a moderately soft volume?

The term that instructs musicians to play at a moderately soft volume is "mezzo piano." In musical terminology, "mezzo" means "medium," while "piano" translates to "soft." Therefore, when combined, "mezzo piano" directs musicians to maintain a volume that is softer than 'mezzo forte' (moderately loud) but louder than 'piano' (soft). This dynamic marking helps to convey the intended emotional expression and nuance in a musical piece, allowing performers to create a rich and varied sound.

Understanding these terms is essential for interpreting musical scores accurately and conveying the composer’s intentions effectively.