A facial expression database is a structured collection of digital face images or video recordings annotated with specific emotional states, affective categories, or facial action units. These collections serve as foundational resources in computer vision, pattern recognition, and affective computing for training, testing, and benchmarking algorithms designed to automatically detect and classify human facial expressions. Media within such databases can be captured in controlled laboratory environments or gathered from spontaneous, real-world conditions, providing diverse representations of basic, compound, or subtle expressions across various demographic backgrounds, head poses, and illumination levels.