How is a Usenet group different from a normal group for ex - a Google Group?

"Google groups are hosted by Google themselves. Usenet groups on the other hand are hosted by a multitude of news servers. They can be accessed using the NNTP protocol. Usually, your service provider also hosts a mirror of some newsgroups. But independent news servers exist also.

In that sense, Usenet is decentralised, wheras google groups is centralised.

It may also be the case that groups created directly on google groups are not synchronised with the other NNTP servers out there (somebody correct me if I'm wrong). I stand corrected."

"Usenet is a set of distributed discussion groups started in 1980 and available through a variety of methods and servers.

Google Groups is a web based service, provided by the company Google, which includes the Usenet groups as well as groups created for its own service."