Facial Action Coding System

The Facial Action Coding System (FACS) is a method used to categorize and describe every observable movement of facial muscles. Developed by psychologists, it breaks down facial expressions into specific muscle activations, called "action units." By analyzing these, FACS helps identify emotions, intentions, or reactions a person may be experiencing. It's used in psychological research, security, and technology like emotion recognition. Essentially, FACS provides a detailed “map” of facial muscle movements, enabling a systematic understanding of facial expressions across different contexts.