@neilNeil Brown
The is more than just the protocol. Diaspora, for example, does not use it and yet belongs to the Fediverse and it is one of the oldest service in the Fediverse.
Fediverse means that instances federate. There are different services: Mastodon, Pixelfed, Diaspora, Friendica, etc. See image.
This diversity has grown bottom up and is also desired by many users of the services. However, there is an app that captures much accounts and displays it in one timeline on the app. This is the Fedilab app: fedilab.app/ @appsFedilab Apps

Since more people are coming to the Fediverse from commercial central platforms, there is often a desire to see everything with one account. For example, the topic was discussed intensively here (in German): mstdn.social/@bsi@social.bund.

Fediverse-Services in a tree with different protocols
source: https://axbom.com/fediverse/
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If you have a fediverse account, you can quote this note from your own instance. Search https://social.tchncs.de/users/werawelt/statuses/115674150584699938 on your instance and quote it. (Note that quoting is not supported in Mastodon.)