The continuous side-to-side erosion caused by shifting of the stream's meanders produces an increasingly broader, flat valley floor covered with alluvium. the flat part of this valley floor, next to the stream, is the

flood plain

Explanation: In simple words, flood plain refers to the low area ground that is adjacent to the river and is subject to floods in situations of high discharge of water stream into the river.

It is formed by river sentiments and usually contains clay, silts and sands that is disposed by he river during floods.

Hence the correct answer is flood plain.