Classical OO design metric (originating with Robert C. Martin) that plots an object's coupling (afferent ↔ efferent) against its abstraction level (general ↔ special). The 'happy' quadrants are afferent+general (utility types like BasicObject) and efferent+special (controllers/orchestrators); the 'sad' quadrants are the absurd inversions. Bellware cites it as a measurable, static-analysis-friendly proof that patterns like fat-model-skinny-controller are structurally wrong, and notes the original name is so abstract it obscured the metric's usefulness — he prefers teaching it via the quadrant diagram.