What term describes a rhythmic or melodic pattern repeated for an extended period of time?

The term that accurately describes a rhythmic or melodic pattern repeated for an extended period of time is "ostinato." An ostinato typically consists of a short musical phrase or motif that is persistently repeated throughout a composition, providing a foundation over which other musical elements can develop. This technique is prevalent in various musical styles, including classical, jazz, and popular music, serving to create a sense of continuity and cohesion within the piece.

In contrast, a theme refers to the main idea or subject of a piece of music, which may be varied or developed but isn’t defined solely by repetition. Variation refers to a technique where the original theme is altered in some way, such as modifying melody, harmony, or rhythm, rather than being a straightforward repeat. A riff, while it can involve repetition, generally refers to a short, catchy musical phrase often found in rock or jazz music but is not necessarily extended over a longer period the way an ostinato is characterized.