Which term refers to an area that is frequently inundated or saturated by water?

The term that refers to an area that is frequently inundated or saturated by water is wetland. Wetlands are unique ecosystems that are characterized by the presence of water, either permanently or seasonally, which supports a variety of plant and animal species specially adapted to such water-rich environments. These areas can include marshes, swamps, and bogs, and play a crucial role in water filtration, flood protection, and providing habitat for wildlife.

Watersheds, on the other hand, are defined as the land area that drains into a particular body of water, like a river or lake, but do not specifically refer to areas frequently saturated by water. Floodplains are areas adjacent to rivers or streams that are prone to flooding, but they focus more on the flooding event itself rather than the consistent saturation reflected in wetlands. Retention basins are designed to temporarily hold stormwater runoff and can aid in flood management; however, they do not naturally occur as ecosystems that are continuously saturated like wetlands do. Thus, the definition of wetland fits best with the characteristics described in the question.