DirectPlay Voice is part of DirectX 7.1. It was introduced with the Windows ME operating system to facilitate voice communication between gamers over a network, by utilizing the DirectPlay session itself. DirectPlay Voice was dropped with the release of Windows Vista.
Other DirectX related glossary:
DirectDraw
Direct2D
Direct3D
DXGI
DirectInput
DirectPlay
DirectPlay Voice
DirectSound
DirectSound3D
DirectMusic
DirectX Audio
DirectX Media
DxDiag
DirectX Media Objects
DirectSetup
XAudio2
