Why is supply a flow concept?

Supply is considered a flow concept because it represents the quantity of goods and services that producers are willing and able to offer for sale over a specific period of time. Unlike stock concepts, which measure quantities at a particular point in time (like inventory), supply focuses on the rate of production and availability that can change continuously. This dynamic nature allows supply to respond to market conditions, demand fluctuations, and other economic factors, making it a crucial element in understanding market behavior.