M3U (MPEG version 3.0 URL) is a file format that aims to store a list of addresses, generally, of audio files and/or video files. Originally created for playlists in Winamp software, these files are simple text files that can be edited by hand (line by line). The m3u seems to be supported by most multimedia player software.
An m3u list is a file in m3u format containing an audio or video playlist. For the purpose of this tutorial, an M3U list is a playlist containing links to IPTV channels that must be read with the VLC player in order to watch TV channels for free.