.stl

The STL format is a standard file format used by Stereolithography hardware and software. Stereolithography, also called "optical fabrication" or "solid imaging," is a 3D printing technology used for producing three-dimensional models, prototypes, and production parts.

STL files contain a 3D design that serves as a master model for creating numerous prototypes. The STL format is an interchange file format supported by several different CAD programs and 3D printers.