Which musical texture describes simultaneous variation of a single melodic line?

The concept of heterophony involves the simultaneous variation of a single melodic line. This means that while the main melody is being played or sung, other musicians or singers elaborate on that melody in different ways. These variations can include changes in rhythm, pitch, or embellishments that all maintain the essence of the original melody but add a layer of complexity and richness to the texture.

In heterophonic texture, each performer contributes their own variations, which can lead to a unique sound that is distinct from other textures like monophony, which features a single, unembellished melody. Homophony, on the other hand, consists of a primary melody accompanied by chords, while polyphony involves multiple independent melodies being played simultaneously. Heterophony stands apart as it specifically highlights the variations of a single melody, making it the correct choice for this question.