It's a discussion group similar to email discussion groups that used to exist in the 1990s/2000s. Members send posts to the group, the group relays it to the rest of the group's followers.

If you're following/posting then it is available on every server.

If you're creating/managing then it does indeed require signing up on a specific server.

Helpful to have your first-hand experience. The original @FediTips phrasing made it sound like a full-fledged feature available in every Mastodon instance rather than "a custom behavior implemented by a couple particular instances."

Still useful in its own right, but not quite as broadly applicable as I'd hoped.

I participate in a few of those, and that is basically it, yes.

If I'm reading that correctly, a "group" is more like an account at particular servers (like fedigroups) that just re-shares out things tagged with the group-account by account-followers; as opposed to being an "every Mastodon instance has Group functionality" that I'd somehow missed.

Would that be an accurate description?

Here you go https://fedi.tips/how-to-use-groups-on-the-fediverse

wait, "follow a group"? I must have missed something here. What are groups? How are they created/managed?