STL (Stereolithography) is a file format native to CAD software created by 3D Systems. It describes only the surface geometry of a three-dimensional object without any representation of color, texture, or other common CAD model attributes. STL is the standard format for rapid prototyping, 3D printing, and computer-aided manufacturing. Sample STL files are essential for testing 3D printing slicers and manufacturing workflows. Developers use them to verify that meshes are "watertight" (manifold) and devoid of holes or inverted normals. They are also used to test the efficiency of geometric processing algorithms, such as calculating volume, surface area, and support structures.