What musical term refers to a two-part musical form where material from section A recurs within section B?

The term that describes a two-part musical form where material from section A recurs within section B is known as rounded binary form. In rounded binary form, the structure typically consists of two main sections: the first section (A) presents a musical theme or idea, and the second section (B) develops this idea or introduces contrasting material, but crucially, it often returns to some part of the initial material from section A before concluding.

This form allows for both a sense of development and cohesion, as it revisits the initial themes, creating a circular nature to the music. It is different from other forms mentioned here. Sonata form, for instance, typically involves a more complex structure with exposition, development, and recapitulation rather than simply recapping a theme within a binary layout. Ternary form features a three-part structure (A-B-A), which differs from the two-section nature of rounded binary. Rondo form generally features a recurring theme separated by contrasting episodes and is structured more around the repetition of the main theme rather than the integration of material from the two sections.

Thus, rounded binary form is characterized by its two-part structure and the integration of recurring material from section A within section B, making it the correct answer.