Auto-Play tag currently shows the following description

> Automatically running programs from inserted discs, USB flash drives, etc.

This suggests that something physical has to start. However, auto play could be for other reasons. 

This question was tagged with `auto-play`. https://superuser.com/questions/1236061/on-a-mac-how-do-i-get-rid-of-disable-html5-autoplay-plugin 

Obviously the trigger for auto-play is when the web page loads (or similar).

Due to the current description of the `auto-play` tag, I removed it from the post.

As I don't like [editing the tags without verification](https://meta.superuser.com/questions/11801/can-we-have-the-option-to-request-approval-when-making-edits) first, can you please vote on one of my 2 answers below (or post your own).