A homography matrix is a mathematical tool used in computer vision and image processing to describe the relationship between two images of the same scene taken from different perspectives. It is a 3x3 matrix that transforms points in one image to corresponding points in another, allowing for tasks like image stitching and perspective correction. This matrix is particularly useful in applications involving camera calibration, augmented reality, and 3D reconstruction. By applying the homography matrix, one can align images, overlay graphics, or reconstruct the geometry of a scene, making it essential for various visual technologies.