SHORT period because of demand exceeding the supply by the MAN MADE factors besides land. It is an ANALYTICAL term in economics, for the income earned, in excess of post-investment opportunity cost, by a sunk cost investment. In general, an economic rent is the difference between the income from a factor of production in a particular use, and either the cost of bringing the factor into economic use (Classical factor rent), or the opportunity cost of using the factor, where opportunity cost is defined as the current income minus the income available in the next BEST use.