This document provides an overview of augmented reality (AR), including definitions, comparisons to virtual reality, how AR works, and examples of applications. It defines AR as enhancing the real-world environment with computer-generated input like graphics or sound. Key points made include that AR combines real and virtual elements in real-time, requires devices like displays and sensors, uses image registration to align real and virtual images, and has applications in medicine, military, education and games. Challenges discussed are performance issues, interaction difficulties, and alignment problems.