When you find channels online or if you subscribe to a service with many channels, each individual channel will have it's own web address.
This is true for paid subscribed channels or free channels that can be found on-line. This is how channels are accessed thru iptv services.
So if you bundle a bunch of channels together and put them into an .m3u file, then that is what is considered a 'Playlist'
Same thing with mp3 music sources, if you gather a bunch of those separate songs up and put them onto an .m3u file, then there you have another Playlist
EPG = Electronic Program Guide, which is self explanatory.