A river delta is a landform shaped like a triangle, created by the deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs at a river mouth, when it enters an ocean, sea, estuary, lake, reservoir, or another river that cannot carry away the supplied sediment. It is so named because its triangle shape resembles the uppercase Greek letter delta, Δ. The size and shape of a delta are controlled by the balance between watershed processes that supply sediment, and receiving basin processes that redistribute, sequester, and export that sediment. The size, geometry, and location of the receiving basin also plays an important role in delta evolution.

A river is a natural flowing watercourse, usually a freshwater stream, flowing on the Earth's land surface or inside caves towards another waterbody at a lower elevation, such as an ocean, sea, bay, lake, wetland, or another river. In some cases, a river flows into the ground or becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to by names such as creek, brook, and rivulet. There are no official definitions for these various generic terms for a watercourse as applied to geographic features, although in some countries or communities, a stream is customarily referred to by one of these names as determined by its size. Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and Northeast England, and "beck" in Northern England. Sometimes a river is defined as being larger than a creek, but not always; in English the language is vague compared to some langauges like French, where a fleuve flows into the sea and a rivière is a tributary of another rivière or fleuve.