.CG File Extension

File written in the Cg programming language, a 3D image definition language developed by NVIDIA; contains source code that defines the shape, appearance, and motion of a 3D model; used by various games and other programs that use 3D content.

Cg is a popular choice for multi-platform 3D content development because its language provides a layer of abstraction allowing developers to target OpenGL, DirectX, Windows, Linux, and Mac platforms without using low-level graphics hardware assembly language.

NOTE: Cg stands for "C for graphics" since it is based off of the C programming language.