Utility:

This is the economist's term for the satisfaction and need fulfillment that people derive from the consuption use of material goods and services.

Stock and Flow:

The term stock referes to a vaiable which has no time demension e.g. 1,000 bags of cement stored in a warehouse pending sales, which can occur anytime. On the other hand, if a variable has time demension, it is called a flow. In other wards, the term flow refers to the quantity of an economic variable measured over a particular period of time. It follows that 1,000 bags of cement produced or supplied per day by a cement company is a flow.