We just call them all forums. We use JIVE for our forum infrastructure. It is a bit odd in its terminology sometimes. Don’t worry too much about this.
But to answer the question…
- A “place” can be either a “space” or a “group.”
- A “space” is one of the public forums in the community
- A “group” is usually a private forum
A group can in fact be public. But we typically use groups for invitation-only private forums. For example, the moderators have a place to go hang out and ask each other questions. Since most of these groups are completely private, you have no idea they even exist. Unless I give away the secret...
As you can see, a group looks and acts just like a "space" or public forum.