Which term refers to a fast-flowing stretch of a river?

The term that refers to a fast-flowing stretch of a river is "rápidos." This word is derived from Spanish, where it literally translates to "rapids" in English. In the context of rivers, rapids are sections where the water flows swiftly over rocks or other obstacles, resulting in turbulent and white-water conditions.

Rapids are significant in navigation, rafting, and ecology, as they provide unique habitats and influence the sediment transport within the river system. Understanding this term is essential for discussions regarding riverine environments, outdoor activities, and geographical features.

The other terms do not relate to this concept. For instance, "descanso" refers to a resting place or break, "snack" pertains to light food, and "duración" translates to duration or length of time. None of these terms are associated with river features or characteristics.