The original seven hierarchies were comp.*, misc.*, news.*, rec.*, sci.*, soc.*, and talk.*. They were open and free for anyone to participate in (except for the moderated newsgroups), though they were subject to a few general rules governing their naming and distribution.
alt.* was not part of the original seven, but created separately as a place with more freedom and fewer rules than the Big 7.
In the mid-1990s, when Usenet traffic grew significantly, humanities.* was introduced, and with the seven hierarchies created by the Renaming, comprises today's so-called "Big 8".
Newsgroup-related matters. This hierarchy was not originally intended for reporting newsevents. It was meant to deal with matters of Usenet in particular