What is referred to when sections in a fugue do not have complete subjects but utilize motivic material?

The term referring to sections in a fugue that do not present complete subjects but instead utilize motivic material is indeed an episode. In a fugue, episodes occur after the initial exposition where the main theme or subject is stated. During an episode, the composer will draw upon smaller fragments, motifs, or ideas that relate to the main subject, creating contrast and development within the piece without restating the full subject. This structural component allows for exploration and elaboration of thematic material rather than just repetition, enriching the overall texture and form of the fugue.

In contrast, the exposition is the first section where the main subject is introduced in different voices. A countersubject involves a secondary theme that accompanies the main subject whenever it appears, providing counterpoint. Lastly, the term fugue itself describes the entire composition rather than a specific section within it. Therefore, the episode plays a vital role in providing variety and continuity in the progression of the fugue.