Which term describes the process of developing a musical theme?

The correct choice is fragmentation, as it refers to the technique of taking a musical theme and breaking it down into smaller, more manageable parts. This process allows composers and musicians to explore different elements of the theme, often leading to new, creative developments within the piece. By focusing on fragments of the original theme, a composer can create variations or develop new motifs that can be woven back into the overall structure of the music.

In contrast, variation involves altering an existing theme to create something new, but it doesn't necessarily begin with breaking it down into fragments. Transposition involves changing the key of a piece rather than developing its melodic content. Extemporization refers to improvisation, where musicians create music spontaneously without precomposed material. While each of these terms is related to music, fragmentation specifically captures the essence of developing a theme through its dissection and subsequent elaboration.