A Discussion object is like a Folder that can contain only Notes (see section 3.3.3).
The basic idea of Discussion and Notes resembles the popular Usenet news. The Discussion corresponds to a newsgroup, the network of Notes replying to earlier Notes corresponds to a thread of articles posted. One major difference is that BSCW lets you control who may read a Discussion or reply to a Note by turning the Discussion into a shared Workspace of its own and by setting differentiated access rights.
In the Discussion's entry in a Folder page or Meeting page, the icon to the left of its name indicates that the Discussion contains at least one Note.
to display the contents of the Discussion in a list below its entry in the current Folder page.
Or
to display the list of Notes in the Discussion page.
Section 4.9 has all the details about Discussion and Notes. It also explains how Discussion objects are used to [Annotate] Documents and URL objects.