A BREP file, short for Boundary Representation file, is a 3D CAD (Computer-Aided Design) file format that stores the geometric and topological information of a 3D solid model. Unlike other CAD formats that might rely on parametric definitions or constructive solid geometry (CSG), BREP files explicitly define the boundaries of the object. This boundary is represented by a collection of faces, edges, and vertices, along with their relationships to each other. Each face is defined by a surface, and each edge is defined by a curve. The topological information describes how these geometric elements are connected, ensuring the model is watertight and represents a valid solid. BREP files are commonly used for exchanging 3D models between different CAD systems and are often used in manufacturing, engineering, and product design workflows. The explicit representation of the boundary makes BREP files suitable for complex geometries and allows for precise calculations of properties like volume and surface area. They are often the result of converting other CAD formats into a more neutral and interoperable format. Because they store the final geometry, they are less dependent on the history of how the model was created, making them robust for long-term archiving and exchange.