Alright, lets sum it up :
- Not made of matter
- Not canon (note : could mean not-in-retail, could mean too abstract to be canon)
- Of human origin (note : we, as players, count as terrans)
- Not comedy-based
- Not an engine feature
- Not an organisation
- Predates Capella (assuming = FS2 era)
- Exists in BP
- Not present in
most campaign
- Not a squadron
- Sort of related to technology
- In a way, it's a game asset
(- You know it when you see it)
"Not made of matter" implies something rather abstract.
"Not canon", "predates Capella (hell yeah)" and "we count as terrans too for the purposes of the answer" suggests it could have some relation to real life.
"Not present in most campaigns", "exists in BP" give us some ways to narrow things down a bit.
"Not an engine feature" but "sort of related to technology" yet is "a game asset, in a way" is a rather confusing set of restrictions.
Let's put aside the game asset bit for now, the fact that it's not an engine feature excludes most modder wizardy & related assets present in BP but absent from most campaigns (fiction pieces, techroom entries, scripting, table values, ...).
"Speaking protagonist" is a nice fit : it's a story telling tool that we are all familiar with, so not an engine feature, has no relation to Freespace canon, is present in BP but not in a number of other campaigns (including retail) and I guess you could consider it a game asset. However, it has no relation to technology and is too abstract to be visual.
"Voice acting" seems better : you need recording tools, so it has some relation to tech without being a strict engine feature and you can see/hear it.
We don't have a lot of questions left (and I could be going in completely the wrong way

), so I won't take that particular shot just yet.
So, knowing it is
not canon, is it still
present in retail FS2 ?