A kind observation that exclusively calling this place "Mastodon" has a bit similar energy as saying "I just sent a GMail."
"Fediverse" (or "fedi") is a more inclusive, general term.
Mastodon is just one of many software projects that talk to each other to create this multi-instance social network:
https://axbom.com/fediverse/
(kudos to @axbom for this fantastic infographic!)
There are blogs, Reddit-like communities, video instances and many more, all part of fedi.

The many branches of the Fediverse
As more and more people are asking me about Mastodon I felt a need for a picture to point at, showcasing how the software known as Mastodon fits into the much larger concept of the Fediverse. I made this infographic to help myself and others explain the many different use-cases






