Wiktionary
n. (context computing English) Any software feature that plays (a video, a compact disc, etc.) automatically.
Wikipedia
AutoPlay, a feature introduced in Windows 98, examines newly discovered removable media and devices and, based on content such as pictures, music or video files, launches an appropriate application to play or display the content. It is closely related to the AutoRun operating system feature. AutoPlay was created in order to simplify the use of peripheral devices – MP3 players, memory cards, USB storage devices and others – by automatically starting the software needed to access and view the content on these devices. AutoPlay can be enhanced by AutoPlay-compatible software and hardware. It can be configured by the user to associate favourite applications with AutoPlay events and actions.