A "Merit Order" is a system used in electricity markets to determine the order in which different power plants are called upon to generate electricity. It ranks these plants based on their production costs, starting with the cheapest sources, such as renewable energy like wind and solar, and moving to more expensive options like natural gas or coal. This approach helps ensure that electricity is produced in the most cost-effective manner, minimizing overall expenses for consumers. The market price for electricity is often set by the last plant needed to meet demand, which can influence investment decisions in future energy sources.