What does the term "modulation" refer to in music?

The term "modulation" in music refers specifically to the process of changing from one key to another within a piece. This process can create a sense of movement and emotional shift, adding depth and complexity to the musical composition. Modulation can occur in various ways, such as through direct modulation, where a piece abruptly shifts to a different key, or through pivot chords, where a chord common to both the original key and the new key is used to facilitate a smoother transition.

The concept of modulation is fundamental in many genres of music, as it not only enhances the emotional impact of a piece but also serves structural purposes by delineating different sections or themes. While tempo changes, dynamics, and instrumentation are all important aspects of music, they do not encapsulate the specific process of modulating to a new key, which is a distinct musical technique.