I still don't understand this, sorry. Obviously you need to use a proper specification:
, or message
, is a single piece of text
, or thread
, is a collection/list of related/grouped messages
is a collection/list of related/grouped topics
are your community, in whole.
So what should not appear and where? What kind of 'posts'?
If you talk about a single topic excluded from the Recent Discussions, it's not possible on the topic's level. Only a certain Forum could be excluded from the Recent list, you may take a look in Manual
how it's done. Probably, you could create a single Forum, where to collect all such "excluded" topics - that's the only way.