What term means to play gradually softer?

The term that means to play gradually softer is "decrescendo." This dynamic marking indicates that the performer should decrease the volume of sound over a specified duration, creating a fading effect in the music. It is often abbreviated as "decresc." or marked with a hairpin symbol that opens to the right.

While "diminuendo" also refers to a gradual decrease in volume, it is commonly considered synonymous with "decrescendo" in many contexts. However, "decrescendo" is the more widely recognized term used for this purpose. "Forte" indicates a loud dynamic level, and "piano" signifies a soft sound, neither of which convey the idea of playing gradually softer. Thus, "decrescendo" specifically captures the essence of gradually diminishing the loudness in a piece of music.