.X File Extension

3D image file used by DirectX technology, which is often used for rendering 3D graphics in games; may contain specifications for meshes, textures, animations, and objects; can be exported using the DirectX SDK plugins for 3ds Max and Maya, or with custom exporters for programs such as Blender and DeleD.

Source code written in the Lex programming language (a standard lexical analyzer for Unix); may be processed with the lex utility included with most Unix distributions to generate a C program; the output is often written to a file named "lex.yy.c."

Lex source code files more often use the .L extension.