The document discusses biometric authentication and gait recognition. It defines biometric authentication as using physiological or behavioral characteristics to identify individuals. Gait recognition specifically aims to identify people based on how their silhouette changes over time as they walk. While unobtrusive, gait recognition is subject to effects of clothing and viewing angles. The document outlines different biometric devices and modalities like fingerprints, facial recognition, and speech recognition. It also describes how gait recognition extracts 1D signals from 2D silhouettes to analyze an individual's walking pattern for identification.