CAD systems allows to save models in several standard formats. Among the available saving formats you may find: .igs (IGES), .stp (STEP), .stl (Stereolithography), .wvl (WRML), .dxf, etc.
Some of them, like IGES and STEP are standard formats defined by committee belonging to different standard bureau; others, like STL and DXF have been defined by companies and then they become de-facto standard due to their broad diffusion.
When using such formats to save a CAD model, you should be aware about the type of information that this format are able to represent.
Different file format may contain different type of geometric information and they are then suitable for different use.
Answered with a tutorial: https://grabcad.com/tutorials/tutorial-how-to-correctly-upload-an-assembly-model-part-3-standard-format