Productive, allocative, X- and dynamic efficiency

Productive efficiency: producing at the lowest point of the average cost curve, where MC = ATC.
Allocative efficiency: producing the output where price equals marginal cost (P = MC), so the last unit is worth exactly what it costs to make.
X-inefficiency: real costs above the lowest possible for that output: slack such as overstaffing or old systems.
Dynamic efficiency: efficiency over time: new processes and products that lower costs or raise quality.

Kraken: Octopus Energy Group and its licensees, as reported by New Power and summarised on Wikipedia (Kraken Technologies). Diagrams drawn with Rough.js and perfect-freehand, both MIT licensed. Your answers are saved only on this device.