The quantity used as the measurement of effectiveness of a system, typically electronic. The figure of merit (FOM) is determined by the primary characteristic that makes something fit for a specific purpose. For example, a digital camera's figure of merit is its sensor resolution, while a loudspeaker's is its frequency response. The figure of merit of an electronic circuit or system may be derived by an intricate algorithm.
MPG is considered a figure of merit when comparing fuel economy of cars, but it doesn't address cost or reliability.