The term 'River Parts' refers to two distinct components of a river system: deltas and mouths. Deltas are formed when a river meets a larger body of water, such as an ocean or lake, and deposits sediment. This sediment builds up over time, creating a fan-shaped landform at the mouth of the river. Mouths, on the other hand, are the endpoints of a river where it empties into another body of water. Both deltas and mouths are important parts of a river system, as they help to regulate the flow of water and provide habitats for aquatic life.