Definition - What does DirectX mean?
DirectX is a suite of application programming interfaces (API) and programming functions used to develop, manipulate and manage graphic and multimedia components in Windows-based software. It is a proprietary Microsoft framework for its suite of Windows operating systems (OS), starting with Windows 95 and through subsequent versions. DirectX includes the following sets of APIs: DirectDraw, Direct3D, DirectPlay, DirectSound and DirectMusic.
Techopedia explains DirectX
DirectX serves as the bridge between the underlying hardware and development platform and helps developers access the underlying hardware's audio and visual capabilities through pre-developed APIs. DirectX is mainly used to develop video games and multimedia applications that require enhanced interaction and automation from system hardware.
DirectX also may be used to access input/output (I/O) functions but is popularly used to create and manage graphical application components. Application creation requires the DirectX Development Kit (DDK).