Reference #319: Thinking in Systems
In a system, a stock is a store of quantity, or an accumulation of some resource. This may be physical, such as water in a bathtub, or intangible, such as motivation or collective knowledge.
Stocks change over time through the actions of flows. A flow may either be an inflow that increases the stock, such as rain into a reservoir, or an outflow outflow that decreases the stock, such as deaths within a population.
Much of the behaviour of complex systems can be understood by knowing the behaviour over time of stocks and flows.
Meadows. Thinking in Systems, 2008. (17-19)RSS