A flow is a collection of production or service routings or a collection of demand streams. A flow represents materials or resources moving through the transformation process, A flow is described by a rate. The measure of a flow is some unit or task per period of time, e.g. barrels per day or service calls
A flow can be a set of operations called a process that accomplishes transformation. A flow can also be a set of individuals creating the demand for the transformed entities. The rate of flow for a process is called its throughput.