The extension .STP refers to files of the type Step 3D CAD files. These are the proprietary files created by the graphics and modeling software, Step 3d which is used for CAD (computer aided design) purposes.

Like many other CAD files, the Step 3d files allow the rendering and modeling of data in a dynamic manner and 2D as well as 3D models of real world objects can be generated using it. The file format of step 3D files is supported by several CAD programs and has good compatibility. This proves to be very useful when model data is to be exchanged between multiple systems. The data format is ASCII and follows ISO standards.