What does the term 'ostinato' refer to in music?

The term 'ostinato' refers to a continually repeated musical phrase or rhythm, making the chosen answer accurate. In music, an ostinato creates a persistent backdrop against which other musical ideas can develop. This technique can be found in various genres, including classical, jazz, and popular music, and serves to establish a sense of unity and stability throughout a piece. For instance, in a piano piece, the left hand might play a repeated bass line while the right hand explores melodic variations. This repeated phrase is essential for creating tension and anticipation, making it a valuable tool for composers and performers alike.

The other choices do not encapsulate the specific meaning of 'ostinato.' A complex melodic structure refers to intricate musical lines that aren't necessarily repetitive, while structured improvisation indicates a more spontaneous approach to music-making without the fixed repetition characteristic of an ostinato. Similarly, while an ostinato may appear in various musical compositions, it does not define a type of musical composition itself. Each of these alternatives lacks the core feature of repetition that characterizes an ostinato.