What is the name of the compositional technique where each voice imitates the melody of the first voice?

The term that describes the compositional technique in which each voice imitates the melody of the first voice is known as a canon. In a canon, one voice presents a melody, and subsequent voices enter at staggered intervals, repeating the same melody, creating a structured and harmonious texture. This technique emphasizes imitation and the interplay between voices, making it a hallmark of contrapuntal music.

The other compositional techniques mentioned offer different approaches to writing music. A fugue involves multiple voices that develop a theme through a series of entries and subject elaboration, but not all voices simply imitate the first voice in the same manner as in a canon. A sonata is a formal structure often used for larger works, such as symphonies, and is characterized by themes and development rather than strict imitation. Theme and variation involves a theme that is played and then altered in different ways, rather than simply imitating the initial melody as seen in a canon. Understanding these distinctions helps clarify why canon is the correct choice for this question.