It stands for HTTP Live Streaming. In this structure, the broadcasting server divides the stream into separate 10 seconds sections of mp4. This is great when the broadcaster requires to stream multiple streaming qualities so that the spectator could use the fitting bitrate of the video considering the network bandwidth.
HLS was formerly invented and used by Apple on their devices. The only downside is that HLS has 10 to 30 seconds of lag so if live streaming does really matter, it is not suggested.
This one has two parts which are MPEG and TS. MPEG stands for Moving Picture Experts Group which was a company founded in 1988 specialized in video streaming stuff and later joined with Adobe. TS, on the other hand, stands for Transport Stream.
This format can provide audio, video, and metadata like subtitle, epg or a different form of data to lock the stream. Mpeg has an error correction feature to keep the integrity of the video whenever the signal is low.