FlowRegion is a class of things whose boundaries are relatively stable but whose constitutive material is continuously moving through the region itself and being replaced by other, similar material. Each FlowRegion is constituted by a stream of matter moving as a whole. A FlowRegion may be liquid or gaseous. A wind may be considered as a Process or as a FlowRegion, similarly an OceanCurrent or a WaterWave. The motion process associated with a FlowRegion F is denoted by (FlowFn F). Note that certain properties belong to the FlowRegion itself (e.g., mass, length, volume, temperature, and speed or velocity of the region moving as a whole), while other properties of interest belong to the Motion of its constitutive stuff (e.g., velocity, direction). The motion of a FlowRegion as a whole (e.g., JetStream moves within the atmosphere) is distinguished from the motion of the pieces of stuff constituting the FlowRegion. See FlowFn and FlowRegionFn.