What is the name when music gets louder or softer?

The name for when music gets louder or softer is called 'dynamics'. Dynamics refer to the variation in volume or loudness in a musical piece. It can be notated in a musical score using specific terms such as forte (loud), piano (soft), crescendo (getting louder), and diminuendo (getting softer). These terms are used by composers to indicate how the music should be performed, creating contrast, emphasis, and shaping the overall musical expression.