Answer Description
Microsoft DirectX is a application program interface (API) used by software developers to create images, animations, and other multimedia effects for video animations and games for Windows Operating Systems. Open Graphics Library (OpenGL) is a similar open source API that is usable on most Apple/Macintosh, Linux, Unix, and Microsoft Operating Systems.
Wikipedia
Microsoft DirectX is a collection of application programming interfaces (APIs) for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms. Originally, the names of these APIs all began with Direct, such as Direct3D, DirectDraw, DirectMusic, DirectPlay, DirectSound, and so forth. The name DirectX was coined as a shorthand term for all of these APIs (the X standing in for the particular API names) and soon became the name of the collection. …
DirectX - Wikipedia, the free encyclopedia