What term is given to a low-lying plain that is composed of stream-borne sediments deposited by a river at its mouth?

A delta is a landform formed at the mouth of a river where it deposits sediment as it flows into a larger body of water like an ocean or lake. The river slows down, dropping its load of silt, sand, and clay, creating a triangular or fan-shaped low-lying plain. Pediplains are erosional plains, peneplains are nearly flat erosion surfaces, and coastal plains are broader features along coasts.