DirectX is an application program interface (API)  for creating and managing graphic images and multimedia effects, especially in applications such as games and video or active Web pages that will run on Microsoft platforms. Program could be written in one of the following object languages: C++, Visual C/C++, or Java.
DirectX is designed so that most of graphic functions can be performed on a graphics card, freeing the main processor for other work.

DirectX consists of the following components:

• DirectDraw - an interface that lets you define and draw two-dimensional images and specify textures. Still used in some games and as video renderer.

• Direct3D - used for creating three-dimensional graphics.
• DirectPlay - for communication over a local-area or wide-area network.
• DirectInput - interfacing with input devices including keyboards, joysticks, or other game controllers.
• DirectSound - integrating and coordinating sound with the images.
• DirectSound3D (DS3D) - used for the playback of 3D sounds.
• DirectMusic - used for playback of soundtracks authored in DirectMusic Producer.
• DirectX Media - comprising DirectAnimation for 2D/3D web animation.
• DirectX Media Objects - support for streaming objects such as encoders, decoders and effects.

Latest versions are:
DirectX 10 - used on Windows Vista (Service Pack 1) and Windows Server 2008.
DirectX 11 - for use on Windows Vista (Service Pack 2) and Windows 7.