Great Renaming
n.
The flag day in 1987 on which all of the non-local groups on the Usenet had their names changed from the net.- format to the current multiple-hierarchies scheme.
Used esp.
in discussing the history of newsgroup names.
"The oldest sources group is comp.sources.misc
; before the Great Renaming, it was net.sources
."
There is a Great Renaming FAQ on the Web.