Question

what is coastal plain

Answer 1

A coastal plain is flat, low-lying land adjacent to a sea coast. One of the world's largest coastal plains is located in southeastern United States.[1] The Gulf Coastal Plain of North America extends northwards from the Gulf of Mexico along the Lower Mississippi River to the Ohio River, which is a distance of about 500 miles (800 km).

See also

Answer 2

A plain adjacent to a coast is called coastal plain.