Which term does NOT relate to tempo or dynamics?

The choice of "repetition" as the term that does not relate to tempo or dynamics is accurate because repetition refers to the act of repeating a particular musical phrase or section, without inherently indicating anything about the speed (tempo) or the volume (dynamics) of the music.

In contrast, the other terms are specific musical indications. "Pianississimo" refers to a very soft dynamic level, indicating that the music should be played extremely quietly, while "fortississimo" refers to a very loud dynamic, expressing that the music should be played exceptionally loudly. "Allegro," on the other hand, defines a quick tempo, suggesting that the piece should be played at a fast pace. These reflect the nuances of how music is performed in terms of volume and speed, directly linking them to the concepts of dynamics and tempo.

Thus, "repetition" stands apart from these terms, as it deals with structure rather than expressive qualities of sound.