Quadric Error Metrics (QEM) is a mathematical technique used in computer graphics for simplifying 3D models. It helps reduce the number of polygons in a mesh while preserving its overall shape and appearance. By calculating the error associated with each vertex, QEM determines which vertices can be merged or removed with minimal visual impact. The method works by representing the geometry of a mesh as a set of quadrics, which are mathematical surfaces. Each quadric captures the error introduced by collapsing vertices, allowing for efficient optimization. This approach is widely used in applications like 3D modeling, animation, and real-time rendering.