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chavaAs for Privacy Groups, my suggestion is Circles. The term was used in G+ for essentially the same thing; to share certain content with a select group of people. It sounds, to me, less tech-oriented and more general audience friendly.
Nextcloud uses the term circles in the sane way. I like it.
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Einer von Vielen a forum (or in future maybe, gyro) is a place, a home, too where other people can subscribe to receive and post messages to discuss, like a mailing list. The support channel is a forum.
A privacy group is what you said: a standard selection of connections I can add to the ACL in one step, without having to add them all individually each time., e.g. all my family members, all my colleagues, my closest friends.