What is the musical term for an increase in loudness?

The term that signifies an increase in loudness is "crescendo." This term is used to indicate a gradual change in volume, where the music becomes progressively louder over a specified duration. Crescendos are often notated in sheet music with a hairpin symbol that widens, indicating to the performer that they should increase their intensity and loudness as the crescendo unfolds.

In contrast, "piano" refers to a soft dynamic level, while "forte" indicates a loud dynamic level. Both serve to describe static levels of volume rather than changes. "Diminuendo," on the other hand, represents a decrease in loudness, which is the opposite of a crescendo. Understanding these terms is crucial for interpreting musical scores and conveying the desired dynamics in performance.