DELTA

(1) An alluvial deposit made of rock particles (sediment and debris) dropped by a stream as it enters a body of water. (2) A plain underlain by an assemblage of sediments that accumulate where a stream flows into a body of standing water where its velocity and transporting power are suddenly reduced. Originally so named because many deltas are roughly triangular in plan, like the Greek letter delta (^), with the apex pointing upstream.