The term relating to a river is 'fluvial, ' which is an adjective that describes something related to or found in a river. It is derived from the Latin word fluvius, meaning river. Fluvial can be used to describe physical features of a river, such as its banks, bed, and flow, as well as the organisms that inhabit it. It can also refer to the processes that occur in and around rivers, such as erosion and sedimentation. In short, fluvial is a term used to describe anything related to a river.