Economic rent is the difference in the amount of money that an individual would be willing to work for, and the amount of money that they are actually paid. Consider a rock star, or a sports figure who earns, say, a million dollars each year, but would actually be willing to work for $100,000/year. Economic rent, then, equals $900,000 which is a payment provided to the individual (or any type of input) due to their "uniqueness". Another way of thinking about this concept is that an increase in wages does not increase the quantity of labor supplied.
More later as this concept applies to any input, not just labor.
