Wall posting
Wall posting takes its name from the ‘wall’. This refers to the channel stream (also known as a personal timeline or profile on other services). This is the stream containing all content published by the channel itself. With wall posting, another user can post directly onto this wall (if you allow it), so that these posts appear in the channel stream. It’s a sort of public personal communication.
It is precisely this feature that forum channels on Hubzilla make use of. Everything intended for the forum is posted as a wall post to the forum channel. And anyone who follows the forum channel (i.e. is connected to it on Hubzilla) will now see everything posted there as a wall post in their stream (their timeline), even if they have no direct contact (connection) with other forum users. Replies to such posts are therefore also distributed to all connections (followers). This makes it possible to run a forum.