There are many variations in the definition of economics. However, all sources relatively agree that economics is defined as, "the social science that studies the production, distribution, and consumption of goods and services." When pertaining to health, Mosby's definition of economics is "the study of supply and demand of health care resources and the impact of health care resources on a population."

Value is defined by Wikipedia as, "an observable measure of its market price." Dictionary.com defines value as, "estimated or assigned worth." Regardless of the source, value is an important core element when discussing economics and is very important when determining the outcome of equations.

Wikipedia refers to marginal value as, "the change in economic value associated with a unit change in output, consumption, or some other economic choice variable. Marginal value can also be defined as the additional value added from the next consumed unit. For example, giving a slice of bread to someone without any would be of great value to them. However, the next slice would not have as much value. The difference between the value of the first slice of bread and the second slice of the bread would be the marginal value.




References:
wikipedia.com
dictionary.com