The economic concept of ___ refers to a state of resource allocation where it is impossible to make any one individual better off without making at least one other individual worse off.

Answer: Pareto Efficiency (or Pareto Optimality)

Named after Italian economist Vilfredo Pareto, this concept defines the absolute maximum efficiency of an economy. When a market reaches Pareto Efficiency, all mutually beneficial trades have been exhausted. Any further reallocation of goods or resources will inevitably harm someone, meaning no net societal welfare can be generated without redistribution.