FACS (Facial Action Coding System)

The Facial Action Coding System (FACS) is a tool used to categorize and describe every observable facial movement by analyzing the underlying muscle actions. Developed by psychologists Paul Ekman and Wallace Friesen, it breaks down facial expressions into specific muscle movements called "action units." FACS helps scientists, clinicians, and researchers understand emotional states, communication, or deceit by objectively documenting facial expressions without interpretation. It provides a detailed and standardized way to study facial behavior, making it useful in areas like psychology, security, and human-computer interaction.