VfW stands for Video for Windows. It was a multimedia framework developed by Microsoft Corp. that was originally an add-on available for the Windows 3.1 operating system. Later on, it became an integral part of Windows 95. It had been developed in response to Apple's QuickTime technology that provided video for Macintosh. From VfW came the Audio Video Interleaving (AVI) container.
VfW also provided an application programming interface for developers who wanted to add video capabilities to their software and provided several tools to edit digital video, though at the time providing a maximum resolution of 320x240 and framerate of 30fps. After VfW came ActiveMovie, which would then later become DirectShow.