A "bank" in the context of a river refers to the land alongside the water. It is the area that borders the river and can be made up of soil, rocks, and vegetation. Riverbanks play a crucial role in the ecosystem, providing habitat for various plants and animals. Riverbanks also help to control the flow of water, preventing erosion and maintaining the river's shape. They can be steep or gentle and may be lined with trees, grasses, and other vegetation. The health of a riverbank is important for the overall health of the river and its surrounding environment.