The .X file is a file extension used by many programs and programmers as a simple mesh file. It is a DirectX file that can be viewed in the DirectX Viewer, a program available with the 2008 DirectX June SDK (Software Development Kit). Although it is not the greatest 3D file format, (not graphically enhanced, moderate quality) it is one of the more efficient 3D model mesh files out there because of how easy it is to load into programs and games.