Which musical term describes the loudness or softness of sound?

The term that describes the loudness or softness of sound is dynamics. In music, dynamics refer to the varying levels of volume in a piece, which can convey different emotions and emphasize certain musical passages. Dynamics help to create contrast within the music and can influence the overall atmosphere of a piece. For example, a performer may choose to play a section very softly (piano) or very loudly (forte), contributing to the expressiveness of the music.

Articulation, on the other hand, deals with how notes are played or sung, which refers to the clarity and movement of the notes rather than their volume. Melody refers to a series of musical notes arranged in a particular sequence to create a recognizable tune. Harmony involves the combination of different musical notes played or sung simultaneously, which creates chords and enhances the melody. Dynamics is distinctly focused on volume, making it the correct choice for this question.