The flat land with a lower elevation than a plain is typically called a lowland.

Here's a breakdown:

* Plain: A large, flat area of land with a relatively uniform elevation. It can occur at various altitudes.

* Lowland: A region of low elevation, usually below 200 meters (656 feet). Lowlands often occur near coastlines, river valleys, or in areas where tectonic plates have been depressed.

While both plains and lowlands are flat, lowlands are specifically characterized by their low elevation compared to surrounding areas.

Here are some examples of lowlands:

* Coastal lowlands: Found along coastlines and often influenced by tides and coastal erosion.

* River valley lowlands: Formed by the erosive power of rivers and usually fertile due to deposited sediments.

* Depression lowlands: Areas of land that are lower than the surrounding landscape, often created by tectonic movements.

The key difference is that a plain can be located at various altitudes, while a lowland specifically implies a low elevation.