In micro-economic theory, the opportunity cost, also known as alternative cost, is the value (not a benefit) of the choice of a best alternative cost while making a decision. Opportunity cost is a key concept in economics, and has been described as expressing "the basic relationship between scarcity and choice.
The law of increasing opportunity cost is the concept that as you continue to increase production of one good, the opportunity cost of producing that next unit increases. This comes about as you reallocate resources to produce one good that was better suited to produce the original good.
A benefit, profit, or value of something that must be given up to acquire or achieve something else. Since every resource (land, money, time, etc.) can be put to alternative uses, every action, choice, or decision has an associated opportunity cost.