M3U
M3U (MP3 URL or Moving Picture Experts Group Audio Layer 3 Uniform Resource Locator in full) is a computer file format for a multimedia playlist.
Extended M3U
The M3U file can include comments. They are prefaced by the "#" character. In extended M3U, "#" also introduces extended M3U directives which are terminated by a colon ":" if they support parameters.
HLS M3U extensions
Apple used the extended M3U format as a base for their HTTP Live Streaming (HLS). It was written in an Independent Submission Stream RFC in 2017 as RFC 8216. Therein, a master playlist references segment playlists which contain URLs for short parts of the media stream. Some tags only apply to the former type and some only to the latter type of playlist. But they all begin with #EXT-X-.
Computer file formats