OpenGL (Open Graphics Library) is a specification
defining a cross-language cross-platform API for
writing applications that produce 3D computer graphics
(and 2D computer graphics as well). The interface
consists of over 250 different function calls which can
be used to draw complex three-dimensional scenes from
simple primitives.
It is very popular in the video games industry where it competes with Direct3D on Microsoft Windows platforms. OpenGL is widely used in CAD, virtual reality, scientific visualization, information visualization and video game development.
At its most basic level, OpenGL is a specification,
meaning it is simply a document that describes a set of
functions and the precise behaviours that they must
perform.
Efficient vendor-supplied implementations of
OpenGL exist for
Windows, Linux,
many Unix platforms, the PlayStation 3, and Mac OS X.
Various software implementations exist,
notably, the open source library Mesa.